my neighbours are in dispute about an extension with their next neighbours. they have asked for a copy of my house deeds to look at and help them with their case. any advice?
Tell them you don't have a copy.
If your land is registered, tell them they can get a copy for themselves at the Land Registry website or by applying in writing, for a few pounds. Anyone can do this on any land - one doesn't have to own it.
Why get involved in someone else's dispute? - you are gonna have to live with one or both parties after the event is sorted.
Because the neighbour's after land title information, I'm assuming (perhaps wrongly) that this isn't about PP. And there's no PP info contained in Land Title anyway