20+ years ago, you could apply for an "easement" to allow this on new
builds and alterations via building control. It wasn't automatically
allowed, but nor was it always rejected. I'm not sure what the situation
is now.

A couple of years ago our BDC officer said it was fine to do it. He said
that before they didnt allow it but as the water company automatically
charge for surface water disposal and you now have to apply for the rebate
that they felt it was now perfectly fair.

Sam