As a local, I agree that Robertsons is indeed a treasure trove for any odds and ends you might need.
However, the jewel in Lancashire's crown is Mathers, based in Bolton: http://www.mathersoflancashire.co.uk/shop.html
Like Robertsons, it's a traditional camera shop, but their film line is much stronger and at really competitive prices. Mail order is first rate, every single order I've placed has arrived the following day, and (like Robertsons) the staff are very knowledgable and friendly.
I can't recommend them highly enough.