I'm not sure quite what qualifies as an "official" soakaway. If it's on your land and it works, then there's no problem with officialdom.

However, if water is already welling up from the ground, this suggests the ground itself isn't suitable for a soakaway, or, at least, it isn't suitable in that particular spot.

The gully you mention - am I right in thinking that it drains onto land that isn't yours? If so, is there some agreement or consent for the gully to operate? Or does it actually drain onto a public highway, the lane you mention? It may be that your simplest option would be to intsall a cheap linear drain, the sort you can get from B&Q for a tenner per metre) as an interceptor at the edge of the concrete hardstanding, and connect that to the gully pipework, and allow gravity to do the rest.

We always work on the basis that no surface water should ever deliberately or knowingly be discharged onto a neighbouring property. I would strongly recommend that you attempt to find some amicable resolution and avoid getting shirty with each other. Maybe a better intercpetor drain is required, or perhaps a length of linear drain connected to a new soakaway. In these situations, the fact that you are attempting to find a resolution is often enough to dampen the fire in the neighbours' argument.

your idea of installing a linear drain at the threshold between your diveway and the public footpath has one fatal flaw - if the surface water system is already flooded and surcharging (technical term for "overflowing" ) where's your linear drain going to drain to?

It might work, if you can outfall the linear drain at some point lower than the floodwater level at the threshold, but, without surveying the site it's not possible for me to say for sure what would work and what wouldn't.

Anyway, if you were to go ahaead with this plan, then responsibility for installation depends on just where the linear drain is sited and to where it outfalls. If it's on your side of the boundary and it connects to the SW system on your property, then the onus is yours, but, if it's actually within the public footpath and/or connects to a sewer on public property, then it's the local council, and you can bet your bottom dollar that they will ummm and aaahhh for a good 12 months before anything happens. If anything happens at all!

For now, I would suggest you contact the highways dept at your local council and ask for a site meeting to review your concerns over the flooding, the re-profiling work and the potential damage to your vehicles using the crossing. They'll eventually send out a totally disinterested technician-cum-inspector and it will be up to you to badger them into coming up with a suitable remedial plan.

Don't hold your breath. I had a similar problem on a property I owned in Wigan and it took the council 5 years to do anything about the surface water that came in through our front door on a regular basis. My lads could have done the job in less than a day, but we weren't official contractors to BigWiggin Metro at the time, and so we had to endure the comedy of errors performed by their DLO that they managed to stretch out to 5 days!

And even then, it still bloody flooded!!

Once the water has run off my neighbours' gardens and onto the pavement, does the council have a responsibility to drain it, rather than rerouting it into my garden?

Yes - if water is draining from a public highway onto your property, the council has a legal obligation to rectify the situation. You should stress this in your letter to the Highways Dept.

Raising the level of the drive and the planter beds will not have any great effect on the groundeater situation. It might make your drive stand proud of any future inundation, but that can't be guaranteed. Given that the floodwaters drained away reasonably quickly, I think it might just work, but I don't think it will eliminate flood risk completely.

Next, to Jim, and your plan to construct an overflow from your soakaway...I'm still not sure how this would work. If the Rain Water Pick-up (RWP) that you intend to connect to is, in turn, connected to the soakaway, then nothing is being achieved. It can only work if the RWP is actually connected to a sewer.

And if it is connected to a sewer, then a better solution would be to route as much surface water to this RWP as possible. How feasible is that?

I know some sectional pipes/ducts and the larger installations normally rely on a bedding layer, but small "service pipes" and armoured cables are just buried in whatever happens to be the local terrain. Responsibility for these services mostly lies with the utility companies themselves (the exception being where they enter private property), so any damage is down to them.

With perforated drainage pipes, some folk choose to lay them in "as-dug" material. It's not something we recommend, unless the as-dug material happens to be a gravel or similar material, but then, no-one inspects land drains, do they?  

taking your Q's one at a time....

1. - 5m is a recommendation, and a good one, but there can be exceptions. However, you can divert the surface water from the area of flooding to the proposed soakaway by means of pipework. Install a gully at the low point in the flooded area and pipe it up to the soakaway.
2. - pumping from a soakaway (which would be more of a sump than a soakaway in this situation) can be uphill or flat. It matters not.  
3. - I can't advise on the use of silicone weatherproofing to a listed building (or any other building!) unless I'm familiar with the site. You need advice from an on-site survey by a specialist water/weather-proofing company.

It sounds to me that you best bet is to install an interceptor drain of some form, maybe a linear drain, at the threshold of your property, that will catch any washback from the public highway, and then to install a gully or similar at the low point in the area where water currently hangs. Pipe this to a soakaway, sump or other outfall as befits the site. If you are planning to discharge onto public/common land, you probably need consent from your local authority. A call to the Tech Services Department should help clarify the matter.

Your architect and/or the BCO for the building work should be able to advise you as to the best remedy for your particular situation. It may require you to re-pipe the sewer, moving it outside the building line, or you may be required to encase it in concrete and bridge it where it passes beneath walls, but, as I can't see the exact layout, it's not possible for me to say what would be most suitable.

Are you building/extending the garage yourself, or will you employ a builder?

The main thing to bear in mind is that there is a simple solution. I've never seen a sewer yet that prevented an extension being built. Don't worry!  

At that sort of size, this must be a public sewer, and so moving it is a much larger operation. It may actually be better to bridge it, which means big money, just depending on the position and orientation of the pipeline relevant to the proposed extension.

Basically, when a sewer is bridged, two padstones are constructed either side of the sewer at least 450mm from the pipework itself. Then, steel-reinforced concrete lintels or a specially cast beam on summat like Holorib steel decking is used to bridge the pipeline, so that no part is in direct contact with the pipework. The concrete foundation is then cast over the top of the bridge. The key point is that the pipeline is NOT carrying any of the load imposed by the new building, which would compromise the integrity of the pipe.

You need to get the BCO involved. They need to approve any plan your builder/designer/architect comes up with.

Good luck!