Apple Spur Pruning

Hi All.
I believe this has been asked before and I have looked at what posts I can find.I also have an old espalier apple tree 12 years + and generally have some nice fruit.Must admit I am late in pruning it and to be honest do not really know how much to prune off last years growth.I have read leave 5-6" and also 2-3 buds,but not sure if this applies to my tree.I have uploaded so photo for you to see the buds etc,I would say the growth from last year is about a foot long.
Thank you

 

Do you know what variety it is, trogre? I suspect it is a spur-bearer if you've been getting good fruit from it, so all you need do is shorten the new growth back to two or three buds (more reliable than length as distance between buds varies).