House bought and paid for by me in sole name - is it always mine?

caprikid1

In summary ignouring marriage there are many ways he can get a beneficial interest in the property.

Contributing to the mortgage.
Acting in a non tenant like manner IE helping with major renovations etc.

In simple yes there  are ways he can a part of your house if you are not careful or marry. I should hasten to add Pre-Nups are not water tight in the UK but judges will consider them when it goes before them.

Some good articles

Beneficial Interest In a Property Explained | Divorce Online (divorce-online.co.uk)

Beneficial Interest in Property | Osbornes Law

In the second article the suggestion of paying or assisting for the cost of a kitchen could achieve a beneficial interest. That said it is unlikely to ever get to 50/50 without a marriage in place.

VyEu

Two things here
1) As a cohabting couple, the basic answer is no, he doesn't have a right
However, the correct answer is no, unless he can establish he has a beneficial interest in the property. Now how can he do this? a) claim that you agreed to give him a share either by directly telling him he had a share and gave him the impression he had a share. No one know what you've said to him etc. and most importantly what is he thinking if and when he moves in? Have the talk *before* he moves in. Burden is on him to establish and bring the claim
b) he contributes to mortgage payments and/or major renovations to the place. The burden will still be on him to claim the interest, and it's not that easy.  

2) if you marry him, if it's the matrimonial home, then default position is he gets half
HOWEVER, that does not by any means stop you from saying that you regard it as a pre-matrimonial assets and therefore he should get less than 50%.
AND strongly consider a prenup. While not legally binding in the UK, provided they are broadly fair (i.e. he's not on the street). you've both had legal advice, and there's full financial disclosure on both sides, they are indicative to a court that the default of 50/50 of *all* marital assets (not just the house) should not be adhered to. 
Again, talk to him about what his and your intentions are going forward and how you want to handle money and buying property going forward (if that's what you want to do one day either by yourself or as a couple)

theoretica

One thing to think about is what happens to his money - if one person in a couple is paying towards the property (assets) and the other pays for the holidays (vanished expenditure) then when they split one person is left claiming the stuff and the other left with nothing... while if you pay attention to ensuring you both build up assets in your own names (if unbalanced from you starting out with the property) then any split will feel fairer and both come out with something.  I guess in summary, I am arguing for him to put the money he would have spent on rent/mortgage into savings and investments in his own name.