Mark Fisher at Leverington Common near Wisbech, can't recommend him highly enough. really knows his stuff. has new and 2nd hand, does alterations, is a Master Saddler, has a menage at his place for trying out saddles, and fits the British Event Team horses... oh, and mine!
he was recommended to me on here too, fwiw.
I've also heard he was good but a friend of mine tried to book him and he was going to be about 4-5 weeks minimum. Ok if you are not desperate but a shame if you are!
Nigel from Robinsons at Billinghay is very good. He fitted a saddle to my duaghter's pony last year, came back 4 mths later to refit and he seemed to know his stuff. He took a long time just standing back looking at the pony before he did anything.
Another person I had out just came and slapped a saddle on the pony's back and said 'that one's fine'. erm - I don't think so.