Blue Horse Travel are based out of Billow Livery, but they may be a bit far up for you.
Or http://www.halcyonhorseboxes.com/ are a new company based out of Sodbury Vale, I used their 3.5 ton lorry at the end of the month for a vets visit. I can not recommend them highly enough, the cheapest I've found, a really nice tidy lorry and Mike is a very nice helpful chap