I was hoping to ask advice on this situation.

I've had some builders in doing a kitchen and garage conversion. One of the things they did was taking out the garage door, digging out the underneath ground to lay foundation and replacing the door with a wall and window.

Our neighbour (in the trades himself) noticed today that they'd filled up the drains with tarmac and dirt/sand.

On the left there was a drainpipe, already missing but the hole remained. They have filled this with dirt/sand. To the right of that was a bigger hole for water to drain down which they've filled with tarmac.

This is likely to cause the water to overflow into my neighbours garage in heavy rain. His garage floor is only very slightly higher than his drive and the water will hit that before his drain.

I texted the builder to let him know and he denies it, saying it was filled when he got there. Unfortunately, while I took video of the kitchen, I didn't take any video or photos of the outside as proof. There's an old photo from one of the house selling websites here but it doesn't show anything clearly. Google Earth doesn't have a suitable photo.

The house is a mirror image of the attached one which has the drainpipe and drain in the same places and there are photos showing the drainpipe (if not the drain hole for rain), so that shows it originally was something there, but all photos are old.

We've not paid the final instalment yet as they're due to finish on Wednesday. They said they'll dig out the tarmac and take a look, but considering they're already denying responsibility it's not looking good.

What would be suggested in this situation? Is small claims court an option if they don't make it right even with the lack of proof? Should the final payment be made or withheld until the matter is settled?