Cheers for the reply, hope you get on well with it. Nikwax also do a cotton gear proofer with UV protection built in. Meant for tents and packs but can also be used on smocks and the likes.
Let us know how you get on once this nice weather finally breaks.
As Mr Fenna rightly said Grangers do some good products too, though personally I'd not use their 2in1 products as we found in tests that they weren't as effective as their single cleaners or proofers which were good. Did all those tests a couple of years back now so they may have improved the product since then.
ATB,
GB.