We use rescue sleds for everything here.I'm sure they'd be available there, they're relatively inexpensive and store away easily. I've been using the same one for over 20 yrs, its made out of sheet metal and wieghs about 45 lbs.
Just to be clear, I'm talking about the sleds that search and rescue teams use to take out injured skiers, hikers, etc. Mine is, like I said, made of sheet metal and is large enough for a moose carcass. 4 men can pull a moose without to much trouble,with a quad or trike its no work at all.
The newer polymer sleds are smaller and lighter and would , I think be perfect for all UK deer.( by the way, its important to be behind the sled when going downhill....... dont ask lol )
Try one out, you might be surprised AB