Help please in selecting a new Espalier apple tree.

RAS

TUVOK

Roughly where is "your area"? As there are often groups which run pruning courses, but only for their members.

Secondly, to repeat what LessImpecunious said

You should not be winter-pruning espaliers.

It is really simple:

When the terminal bud forms in late summer, cut any new growth over 125mm long (this year's) back to three buds above the annual ring although you can womble that to 2-4 buds if that allows you to choose a bud facing outwards. 

The following year those buds should break to form:
a new shoot from the top bud
a little spur
A fruit bud from the bottom bud

BUT Discovery is a partial tip bearer so it is important not to remove all the fruiting buds on the tips. 

One of my espaliers is a partial tip bearer, and I get decent quantities 3 years out of 4. I now prune back new strong growth to three buds in the late summer and leave the shorter branches until spring. If they've got a fruit bud on the end (you can wait until they start to burst) leave it. If it's a shoot, cut back to three buds.

I also leave spur thinning until I can see what's a fruit bud and what's going to be a shoot, and cut back above a fruit bud. 

TUVOK

Thanks for your helpful comments.
My area is Newport, South Wales.
I'll go back late summer and try again.
It just seems a blind spot with me, it's annoying as in early years mass's of blossom.

RAS

Keep an eye on Bringing our orchard expertise to Swansea! - The Orchard Project

Ask them about any groups offering pruning courses?

I would say that the level of expertise in orchard management varies but they may well know someone who knows someone..

And accept that summer pruning is less well understood because people don't grow espaliers as often as "trees."