OK - essentially, pre-nups don't carry the legal weight in the UK that you might think.
Let me set things out for you here.
The starting point is that any property owned prior to marriage is not considered a marital asset.
Should the relationship breakdown, and you look to divorce, the position is that this presumption would only be departed from if it was necessary to meet the needs of one or more of the parties and it was deemed fair in the circumstances. This departure from the presumption would also override prenup.
So whilst you can sign a prenup, and this will be 'more' legally binding if it is entered into with independent legal advice on both sides, there is always the chance that a judge can depart from the agreement in the divorce settlement if it is deemed fair to do so.
This is the law as it stands currently, but the law is an evolving beast!
As to the laws of other countries, I cannot offer advice there.
Is there anything I can clarify about this, as far as the UK position stands, for you?