Mak,
Don't overlook Barrow - Walney Island. Interesting field, 2 tarmac runways.
I did some gliding out of there a while back and stayed in the control tower building - Lakes Gliding Club, if I remember right.
There's also Carlisle, which is supposed to be a good GA friendly field.
If I were planning the flight, I'd go up via Gamston, Sherburn (not necessarily stopping there, but useful diversions), turn left at Harrogate towards the lakes. Avoids all the built-up area around Man/Liv etc.
A word of caution - the evenings do draw in pretty fast in August, don't be too ambitious if leaving at 17:30 from Denham. You may be in reasonable light at 3000', but when you descend to land it may suddenly seem a lot darker. Watch out for mist as well.
Have a good flight!
SD