Air Asia doesn't hire expat FOs. Therefore, you're talking about Lion Air and Vietjet. Therefore, you're talking about two of the worst and !!!!tiest pay-to-fly schemes on the planet, that will get your CV promptly thrown in the trash by a very large percentage of chief pilots, if your intention is to return to the UK after you've done your hours.
My advice to you is simple, don't do it, even by the standards of pay-to-fly, there's a lot better schemes out there than either of those two