Well, I'm just back from a lovely week visiting my father and stepmother in Cornwall and I thought I'd share my experiences for anyone else travelling.
Positives
I stayed one night in a Holiday Inn Express and found them excellent, the breakfast had gluten and lactose free options available.
We had lunch at a cafe called On the Bay in Penzance where all the food was cooked to order and everything was gluten/wheat free. Also the staff were great and really willing to help and accommodate food issues. I had fish and chips for the first time in 2 years!
I found a new business called the Cornish Field Kitcken who make the most amazing gluten free sticky toffee pudding and also offer it lactose free as well. They do mail order and hope to have the lactose and gluten free pudding available to order soon.
I also found a services just north of Exeter which had gluten free options but I have forgotten the name of the place. Maybe someone knows it, I feel they deserve a mention.
Negatives
I stopped at Annandale Waters Road Chef coming north. Sadly the only option available to me was sweet snacks, such as cakes, or macdonald chips (yuck) and a macdonald side salad which consisted of a handful of lettuce and 2 slices of cucumber (I can't eat raw tomato). Needless to say I was starving by the time I got home at 6pm.
Over all food wasn't too difficult away from the service stations and I feel very grateful to the restaurants and businesses who make an effort to help those of us who have food issues.