Discharge to a highway drain: the authority's position
A road gully looks like the easy answer for surface water. The highway authority owns that pipe for the road, not for your plot, and consent is discretionary.
There is no right to discharge to a highway drain. That is the whole position in one sentence, and it is the opposite of what most self-builders assume when they look at a road gully three metres from their new driveway. A connection to a public sewer carries a statutory right under section 106 of the Water Industry Act 1991, subject to limited grounds for refusal. A connection into highway drainage carries nothing of the kind. The highway authority owns that pipe for the purpose of draining the road, and it decides whether anything else may enter it.
So the sequence is consent first, then design. Not levels first, then a hopeful email.
Why a highway drain looks like the answer
On a tight plot with clay subsoil, a gully in the kerb line is the only visible outfall. It is close, it is already there, and it is at the right depth. The alternatives all cost money: a soakaway needs porous ground and space, a watercourse may be 80 metres away across someone else's field, and a sewer connection means a road opening in the other direction.
That logic is understandable and it is also how schemes end up with an undeliverable drainage strategy approved by nobody. A planning permission conditioned on details of surface water disposal is not consent to connect to the highway, and the highway authority is entitled to say no after permission is granted.
The highway authority's position on new connections
Ask a county drainage engineer and you will hear three objections, in this order.
Capacity is the first. Highway drainage is designed for the impermeable area of the carriageway and footway, often to a one in one year or one in five year standard rather than the one in 100 year plus climate change standard a development is held to. Adding a plot's roof and driveway to a system already running at capacity produces surcharging at the low point of the road, which the authority then has to fix.
Liability is the second. Once private water is in a public asset, the authority carries the consequence of a blockage or a flood, and it has no control over what happens upstream of the connection. Silt, oil and building debris from a domestic driveway all end up in its gullies.
Precedent is the third, and it is usually unspoken. An authority that consents to one connection in a street will be asked by the next six applicants.
None of those is a reason to give up. They do explain why the response to a bare request is almost always negative, and why a request supported by infiltration test results, a flow calculation and an offer of treatment gets further.
Consent and agreement routes
Establish who owns the asset before anything else. Ask the water and sewerage undertaker for its sewer records and ask the highway authority for its drainage records for the frontage. Three answers are possible.
- The gully discharges into a public surface water sewer. The section 106 right to connect applies, with the undertaker as the decision maker, and the highway authority's role is limited to the works in the road.
- The gully discharges into a highway authority drain that outfalls to a watercourse. Consent is discretionary and comes from the highway authority.
- Nobody has records. Common on unadopted roads and pre-war estates, and it means a survey with a camera before any design work.
Where consent is given, the works themselves need an agreement. Anything within the publicly maintainable highway is caught by section 278 of the Highways Act 1980, which sets the design standard, the security bond, the technical approval process and the fees. Some authorities deal with a single gully connection under a minor works licence instead. Expect to pay for design checking and site inspection either way, and expect the programme to run to months rather than weeks.
Remember section 163 of the same Act as well. An occupier must prevent water flowing from their land onto the highway, so a driveway that sheds water into the kerb without consent is a problem in its own right, not a solution.
Where a connection is refused
A refusal is information, and it belongs in the Drainage Strategy as dated correspondence. The strategy can then show the authority's position as a fact rather than an assumption, which is what a lead local flood authority consultee wants to see before accepting a lower option in the hierarchy.
What does not work is treating a refusal as a reason to design nothing. On a small site with no outfall, the answer is usually a combination: reduce the impermeable area, hold water on the plot, and release it slowly at a rate the receiving system can take.
Alternatives to test first
Work down the hierarchy in Planning Practice Guidance on flood risk and coastal change, and document each step.
Infiltration comes first. Test it to BRE Digest 365 with trial pits at the proposed soakaway location and depth, not a single pit by the gate. Record the date, the groundwater level and the soil description. Clay does not automatically rule infiltration out: shallow permeable made ground over clay sometimes works for a small roof area, and a lined permeable paving sub-base with a controlled outlet is a different proposition from a rubble filled pit.
A watercourse is next. Discharging to an ordinary watercourse needs land drainage consent for the outfall structure from the lead local flood authority under section 23 of the Land Drainage Act 1991, and riparian consent from the owner of the bank. A main river outfall involves the Environment Agency. The presumption against burying a channel matters here too, which is why discharge to a watercourse is worth exploring before a culvert is considered.
Then the sewer. A surface water sewer connection under section 106 is the most reliable route where one exists, and the undertaker's grounds for refusal are narrow. A combined sewer is the last resort and undertakers increasingly resist it.
Storage sits alongside all of these rather than below them. Water butts, permeable paving, an attenuation cellular tank under the drive and a flow control at the outlet are the ordinary tools, and rainwater harvesting and attenuation credit can shave the volume a small site has to find.
Pumped discharge is possible and unpopular. Most authorities treat a pump as a maintenance liability that will fail, and will only accept it where gravity cannot work and the pumped element serves a small area with storage upstream.
Evidence for the planning submission
For a single dwelling, the pack is short. A drainage layout showing the proposed system, a calculation of the impermeable area before and after, infiltration test results with trial pit locations, the discharge rate and the storage volume, and any correspondence with the highway authority or the undertaker. That set is the core of drainage evidence for a single new dwelling.
For anything in Flood Zone 2 or 3, or on a site of one hectare or more, the drainage case sits inside a Flood Risk Assessment along with finished floor levels, exceedance routing and residual risk. Where surface water on the road is the flooding mechanism, say so and show where water goes in an event beyond the design standard.
Two details are routinely missing and routinely asked for. The first is a maintenance plan naming who cleans what and at what interval, because a SuDS feature with no owner is a refusal reason. The second is an exceedance plan showing the overland route when the system is full, which for a highway connection means demonstrating that surcharge does not back up into the driveway or the garage.
PlanScope drafts the Drainage Strategy and Flood Risk Assessment narrative from your site data and the answers you give in the guided flow, with a flag inserted wherever a site-specific figure such as an infiltration rate is still missing. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. For specialist technical reports, qualified professional input may be required, and hydraulic calculations should be checked by a drainage engineer.
This is general guidance, not legal advice; check the position with your local planning authority, the highway authority or a qualified professional before relying on it.
Enter your postcode on PlanScope to see whether your site sits in a flood zone and which drainage reports it is likely to need.
Frequently asked questions
Can I connect my new driveway drain to the road gully?
Only with the highway authority's written consent, which is discretionary and often refused. The highway drainage system is sized for the carriageway it serves, and taking private water into it transfers both capacity risk and maintenance liability to the authority. Ask before you design the levels, because a refusal after construction leaves nowhere for the water to go.
Is a highway drain the same as a public sewer?
No, and the distinction matters. A highway drain is a highway authority asset, usually maintained by the county or unitary authority. A public surface water sewer belongs to the water and sewerage undertaker. Gullies frequently discharge into a public sewer, in which case you may have a right to connect under section 106 of the Water Industry Act 1991 instead.
What is the surface water discharge hierarchy?
Infiltration to ground first, then discharge to a surface water body such as a watercourse, then to a surface water sewer, highway drain or other drainage system, and only then to a combined sewer. Planning Practice Guidance and most local plan policies expect you to demonstrate that each higher option was tested and failed before the next is accepted.
Do I need a section 278 agreement to make a connection?
If the works are within the publicly maintainable highway, yes. Section 278 of the Highways Act 1980 covers works to an existing highway carried out at a developer's expense, and the agreement sets the design standard, the bond, the fees and the inspection regime. Small connections are sometimes handled under a minor works licence instead, which the authority will confirm.
What if infiltration will not work on my site?
Test it properly first, to BRE Digest 365 or an equivalent method, and record the results with the trial pit locations and groundwater levels. Clay and high groundwater are common reasons infiltration fails. With that evidence in hand the authority has to engage with the next option in the hierarchy, which may be a watercourse, a sewer connection or attenuated discharge.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.