What I think you are saying is that your partner wants to hang onto the property and only give the X the 35% when he decides to sell it. Is that what you are getting at?
Whilst it doesn’t say it in exactly these terms, clauses 4 and 5 and 6 are clear enough.
4 Ms XX wishes to assign her beneficial share to Mr XX for which he is obliged to pay the amount of her interest.
There is no provision for the person not wanting to take the assignment but clause 6 says that if neither wishes to assign (it doesn’t mention except the assignment) the property shall be sold.
He may have grounds to contest the deed on the basis that he didn’t realise the nature and effect of it if it was drafted by her solicitor and simply stuck in front of him. However it seems likely that his solicitor was advising him with regard to the transfer.
What I also don’t know is why he gave her the 35% and whose idea that was.
I’m not certain whether that answers the question for you or not but I am happy to answer any specific points arising from this. You may get the impression the thread closes after rating, that it does not, it remains open and we can still exchange emails if you wish.