Thank you for the comprehensive response. Yes, tried transdermal route very early on in my quest to figure this out. Whilst it worked well in terms of raising D level, it gives the same symptoms as taking supplements any other way. Symptoms of weakness, fatigue and brain fog set in rapidly with as little as a supplement of 400iu daily. This happens by the third day of 400iu. Over the last few years, I've tried every brand, type and method of supplementing, all with the same result.
GP doesn't believe this intolerance is possible. On my request he tested for calcium / parathyroid issues and lyme disease in case any of these were the underlying problem, but all ok. So he's ignoring the problem even though I'm deficient at this time of year.
I'm unable to consume fermented foods including dairy, due it it triggering flare-ups of another disorder I have, so the yoghurt idea is out
Regular holidays to sunny climes are out for various reasons, so it looks as if I will have to find a suitable UVB source. Cholesterol level was around 6 this time last year. Not too low to make D via the skin I hope!
If you come across any further info relevant to people with D supplement intolerance, I would be very keen to hear about it. I know I'm a bit of a rarity, but there are others in the same situation and it seems to largely be being ignored in all the vitamin D research.