Glad to hear we are not the only ones! Although we have had this problem for around 10 years and ever since we had the boiler changed to a combi and the water storage tank removed from the loft. We contacted the 'so called experts' around about a year later when we first noticed the problem, they advised we have some additional ventilation put in the loft, which we did at a cost of around £500.00 - it didn't make a jot of difference and at the time, we didn't get them back in, not sure why, may be as it was approaching the warmer months where we didn't require the heating on. I have since done as others have recommended on here, and pulled away any insulation that might have been blocking the eaves, still made no difference.
The house I believe was built in the 70's (would need to double check) and is a typical 3 bed detached with single garage, it has this horrible plastic lining on the inside of the loft roof where the condensation runs down and drips from. I am sure this is needed, but I'm no expert so couldn't say what for. I'll post a pic and short video I took recently when I have more time as we tried to see if it had improved during the December cold spell, but it hadn't, wishful thinking! The only thing that we have found, as a cheap and cost free solution, is to leave the loft latch open. Not fully, just at a bit of an angle with about a 4-6 inch gap. This is not good for keeping the house warm though as all of that lovely heating goes straight out, but it does keep the roof dry and we figured is cheaper than a new roof!
If anyone can recommend a roofing expert, that is trust worthy and not a rip off merchant, in the Nottingham area do let us know as I'll happily call them out for advice and to see what can be done. I hate having the loft hatch open all the time - October - May depending on how warm it is. It shouldn't be necessary and when the wind is blowing strong and in a certain direction you get the upstairs smelling of that lofty, fusty smell, which is not pleasant.