Thank-you for all the responses. My original post was truncated, but you seemed to have gotten the gist!
I have been in touch with George Fisher as they have a podiatrist in sometimes and seem to offer a specialised boot fitting service. I'm in Surrey so it's a trek to get t here, but worth it if I can solve this problem. The only solution I have at the moment is pre-emptive Compeed, which usually works but has to be fitted just so or I still get problems.
I'd prefer a better solution which I suspect may be a more appropriate fit, probably coupled with some exercises (I understand tight calf muscles can exacerbate this). I'll investigate the other ideas and shops above. I was once told I have narrow heels and that the Brashers were not an appropriate fit (poor advice from original shop - not named here).
I don't mind travelling and spending a reasonable amount on boots etc, but don't want to be back to square one the first time I go for a walk in them. Thanks again.
I believe that the visiting podiatrist at Fishers is Andrew from Rebound Clinic. I visited his place in Settle for a full analysis and supply of custom made insoles to cure a severe metatarsal problem. It was expensive but did the trick. You could try calling him direct before travelling either to Keswick or Settle to see him.
Just stayed at Cwmdu campsite with my caravan and did bits & pieces of the Beacons Way. Campsite mainly seasonal caravans but lots od space for tents. Toilets & Showers etc. Had reasonable meals at nearby Farmers Arms & Mynydd Ddu Tea Rooms.
I'm not sold on stand-alone GPS units and favour either a Smartphone or 7" tablet which provide more uses. The latter has a bigger battery than my Smartphone and lasts all day. If you still have access to your Anquet maps through their "cloud" services then I would suggest you look at this used in conjunction with a 7" tablet.