Thank you for your question
My name is Clare
I shall do my best to help you but I need some further information first
Who actually owns the UK house and which part of the UK is it in?
How much have you personally spent on the property?
I appreciate all of that - but I need to know what structural alterations and improvements you paid for and how much they cost
I am afraid that there are no such "defacto" laws in the UK.
In the UK co-habiting partners have very very few protections whatsoever.
Where property is concerned the only claims that can be made are via property law.
Whilst the courts have stretched the boundaries as far as possible in terms of intention the fact remains that your only claim is based on any financial contribution you have made to the bricks and mortar.
Paying for the shopping and the bills does not give you a share of anything
In reality you have two possible basis of a claim.
There is the promise of "provision" which gives rise to a potential claim of "proprietary estoppel"
This essentially means that you acted to your detriment (which you clearly have) on the basis of a promise of a share in the property.
There is more about the doctrine in the article here
My concern regarding this is the ambiguous nature of the word "provision"
In addition under property law there is an Implied Trust that arises when you pay for or do work on a property that enhances its value
More details here
Your starting point is to try and discuss matters with him using Family Mediation
however if that is not viable then you may need to consider a court applictaion the process is described here
fBizarrely if he dies you will be better off as the courts would then be likely to award you half of the house
Sad;y we have a long way to go to catch up with our Commonwealth cousins.
Please ask if you need further details