Inside the UK, if a couple had only an Islamic marriage and did not register civilly, then civil divorce is not required and an Islamic divorce certificate will suffice. If this is not the case, then both a civil and Islamic divorce are required. If the couple married outside the UK, then both civil and Islamic divorces are necessary to finalize the matter. It does not matter whether the spouse was sponsored to UK or not as the marriage is legally valid as long as it is recognized by the country it took place in.