A couple summers ago we found these great books called Wild Swimming and Wild Swimming Coast. Since then we have parked our car in tinier than tiny woodside car parks (or roads) and walked narrow footpaths to find some of these (sometimes) hidden treasures.
We have swam in a quarry in the Malverns, found sweet rock pools and beaches that we would have never come across had it not been for these books.
I would highly recommend getting a copy.
Let the adventures begin!