Don’t worry about the groupset as even Sora is pretty good now, instead take a good look at the fit of the bike, the ride, the frame and the wheels, in that order. Road bike components don’t wear out anywhere near as fast as a mountain bike, the key issue will be your fitness which will get better as you ride them more, provided you actually enjoy riding on road!
If you like the bike you will be riding longer distances on it too.
Lots of really good road bikes available for £850 so don’t worry about the budget unless you desperately want something super lightweight. There are some pretty good Carbon bikes are on special offer at the moment but the alloy frame/carbon fork ones are really good too so you’ll actually be spoilt for choice.
Also don’t forget some shoes/pedals though basic Shimano SPD R’s are dirt cheap and work very well, as for shoes, Wiggle and Dhb is your friend!