There was documentation to the marriage? Because I really question the legal in Britain thing. If no marraige was filed legally, how was it legal? From every account I have read, it was strictly a religious ceremony with no legal filing. It was the islamic way to get around polygamy laws they lived under when they were still under British law/rule.
Please review the law at the time in the country in question. The country has a searchable database that will also inform you about the laws concerning tribal marriages versus civil marriages.
It was a legal marriage.
You can choose not to believe it or do the research.