I'm in the UK too.  I know you asked about a free site, but I
subscribe to www.weightlossresources.co.uk which costs £9 a month. You
can sign up for a free trial for 3 days though, which would give you
the chance to look at calorie values for almost every UK food product
you can think of.  I don't know of any free sites, but there may be
some.
I've just read the above and I sound like a spammer, but I've been
here on asd for several years and I can assure you I'm not:)

janice