+1 for Grenson, and Tricker's are good boots, but very expensive. The other bootmakers, who are still making them in Northampton, are NPS-Solovair. Their boots are about the £250 mark, with Goodyear welts, and very good, if you can get over their being named named after some of my least-favourite British Prime Ministers. They are a bit hard to get hold of, as they don't have too many retail stockists, but they do sell on-line (when they have stock).
Although I guess you really want to "Buy British", some of the best boots I've had are Red Wings, which are genuinely (unlike e.g. G. H. Bass-made in China) made in the USA.
The biggest problem I've had with any boots that are stitched through to the sole is finding someone to repair or resole them. Being from Suffolk, I hate to have anything that's not repairable.