First port of call the local relevant authority online planning site. Most if not all of the LAs have brilliant sites with full planning records and maps.
The Land Registry has the details of who owns what but, and someone can correct me, I think there may be conditions about what you can and can't see as a not specifically interested party i.e. neighbour, owner, etc. I guess you could check out the Land Registry website for their terms and conditions before you spend time popping into to them.
Of course you can always get a solicitor to do a full search for you in advance at a cost above what you might pay with the DIY job if you are just speculatively interested.