No personal experience, but I would probably talk to a mortgage broker rather than applying directly to a bank or building society, as a lot of their lending is entirely computer tick-box based. You'll need to find somewhere that has an actual person making the loan decisions. The FCA essentially required banks to have actual proof of income before making loans, post the 2007/8 crash, so the "self-cert" mortgages of the past are no longer a thing and you will need to show that your assets do indeed reliably produce an income sufficient to cover living expenses and the loan costs.
