There are rumours the government may double cgt in the UK. At the moment:

If you make more than your personal allowance in income - you have to pay 20% cgt
if you make less than that in income you have to pay 10%

(I think it's based off income but not 100% sure).

You buying a house with bitcoin will depend on a buyer being willing to accept it. Its happened before afaik but might an unlikely goal to secure any property you want with it.

If you pick a solicitor right you can probably use bitcoin as a proof of funds but sales also take 6 weeks to go through so you likely won't get an optimal price to pay keeping your funds in bitcoin during that time (and bitcoin is less reversable and less traceable than fiat do there's a risk there too).