No offense but you'd have to be a total idiot to buy real estate with bitcoin. We are still in the era of fiat mining. Not even the richest 0.001 percent pay hard cash for real estate unless of course they are in a huge hurry and willing to take a loss. Get some money counterfeited by the bank for you, er, I mean get a loan!
If the UK housing market crashes and you have a mortgage is that better vs cash purchase? (you'd have negative equity but i guess you can dump the mortgage is that the advantage?)
Also with cash buys you get on average 7% cheaper purchase to begin i have read.
There have been a couple of replies here re: tax treatment of UK property purchases (i.e. doesn't matter how the transaction was performed, registry for ownership requirements etc.) that sound like they know what they are talking about. If you're keen on living on the bleeding edge and setting new precedent, then my advice (IANAL) would be to check out existing legal precedent for house purchases made with other commodity assets rather than with exchangeable currency.
In other words, check out precedent for house purchases made using gold. This, here in the UK, should be easy enough as it surely isn't a rare situation. There's a lot more resistance in the UK for Bitcoin to be seen as a currency rather than a commodity / asset (for some reason - try opening a bank account for a Bitcoin business, for example), and if a formal argument had to be made (i.e. you argued with HMRC and took a Bitcoin-related tax case to the Tax Commissioners for arbitration) then I'd expect Bitcoin to be 'deemed' to be a commodity asset rather than a currency, in line with the American IRS opinion of Bitcoin.
However, the most important aspect in the UK for the capital gains treatment of property is whether the house is your primary residential dwelling or not. I haven't noticed in your posts whether you've mentioned this or not. If you're planning on buying your primary residential dwelling (you said you're currently renting, so perhaps your first home?) with Bitcoin, then you shouldn't need to pay CGT on any house price gain when realised on sale. No matter how you buy the house, if it's your primary home then you don't pay CGT - certainly not in my experience.
This, of course, assumes that the UK residential housing market will net you a gain in the near future, which is a very dodgy assumption anywhere outside of central London (which is a global market and disconnected from the rest of the UK housing market).
If you're buying commercial property or a buy-to-let residential investment property, then that's taxed like any other investment in the 'property' asset class.
If you're talking about the CGT deemed on the value difference between the Bitcoins when you first acquired them versus the final purchase price of the house (as per Land Registry registration, which you'll have to do when taking ownership, as pointed out above)... well this is the tricky bit. You'd have to declare the Bitcoins on your self assessment tax return as an asset, and you'd have to be able to value the Bitcoins as at original price of acquisition. If you mined them, then they're not free since you'd have paid for the mining hardware and the opportunity cost of doing so. If you acquired BTC early on in the game, valuation against GBP would be vague as hell because unlike most commodity markets, there is no price fix for BTC. And unlike now, with reliable exchange markets, there was no easy valuation / GBP exchange (well, Britcoin / Intersango worked for a while a few years back, but whether their 'market price' history would work in a tax court is open to debate).
Equally, I'm not sure whether Bitcoin has any guidance for asset valuation / tax treatment from HMRC (I'm not a tax lawyer, just a freelance consultant who has had to do my own company tax returns for over a decade). If there's no exclusion then I'd expect a similar treatment to gold, for the reasons stated above.
However, you'd have to declare this on the tax return, as in most other Bitcoin related trading, there's no easy way for HMRC to track Bitcoin capital gains by UK tax residents. Currently, I expect most of us in the UK don't declare Bitcoin (or any other altcoin) gains...
But being the first person in the UK to buy a *residential home* with Bitcoin would be a big story for the media here. If you didn't keep it completely secret, then I'd expect the story to be all over the national press (for non-UK residents, talking about the housing market here is a national pastime). And you can bet your life that the taxman would pick up on this. Given that you need to involve other parties (solicitors, Land Registry, the counterparty selling the house) when buying a house, keeping the transaction secret could prove rather difficult.
TL;DR - Unless someone's already bought a house with BTC in the UK, you're going to be news, and the taxman will know about the transaction purely that way. So the probability is high that you'll end up a test case for Bitcoin CGT treatment by doing this.
But I applaud your sentiment re: diversification - if your entire net worth is currently Bitcoin holdings, then you're taking a big risk and - with the volatility of Bitcoin - loads of emotional stress watching the value gyrate. UK residential property though? Have you considered buying some gold coins with the Bitcoin? Easy enough to do - plenty of reliable people selling bullion for BTC (I started off selling my mined BTC for silver and gold bullion in 2011...) - and if you wish, discreet enough to not declare to the taxman. Gold is currently cheap...