There is a strong culture in many countries where family abroad is expected to fund family back home.
It’s a pride and cultural thing.
A lot of times the men involved are very obedient to their parents. When they marry the wife is not the centre of her husbands world, she’s below his mother in the pecking order. So when the mother says jump the man says how high. The wife just has to accept it. As that’s what happens in the culture.
There’s another thread on her regarding the same type of thing, a man sending so much money home that he and his wife live in relative poverty and his non working lazy brother and wife who has five kids live off the money he sends back to his home country.
It’s nice to help family. But to lie about it is unacceptable. What he wants to do with his share of your joint money is his business. But you should still have your half of the monthly pay to do your thing.
For me that would be a dealbreaker. Is your marriage legally recognised in the U.K., ie a paper marriage not just within Islam? If so you and this is a deal breaker for you, I’d be considering divorce. I couldn’t live with a liar. That way you’d get half of everything including the house (although granted it’s more complicated than that and depends on a number of factors).
You either accept this culture and realise he can’t change its ingrained. Or you try and get him to be fair to you and watch him squirm and potentially hide more things from you. He may be able to change and tell the family he’s not a cash cow, some have per other threads. But it will be hard and his family will threaten to never speak to him again and be wailing down the phone about how terrible a man he is yada yada.
Perhaps he should give the flat to his brother and tell him no more money will be forthcoming for anything. Ever. And then you start again saving for a flat? Without having to send money home you should manage more quickly than five years this time.
But I’d imagine you’d need to keep an eye on finances as the minute the mother says she needs money he will be transferring it over like the “good son” he wants to be.