Margaret Thatcher concerned over 'second wives'
Margaret Thatcher was strongly opposed to admitting women to the UK who were the second wives of men in polygamous marriages, Cabinet Office files show.
The then prime minister also believed there was a danger of the government favouring "the coloured Commonwealth" at the expense of the UK if it did so.
The newly-released file covers immigration policy from 1982 to 1986.
The document shows the issue of admitting second wives created constant difficulties for Thatcher's government.
It was worried about how Commonwealth countries, the European Court of Human Rights in Strasbourg and its own MPs would react to changes in policy.
It discussed the merits of introducing visas for Commonwealth immigrants in order to control numbers, and to move the queues of people wanting to enter the UK from Heathrow to their countries of origin.
And it discussed new powers to take action against exiles in the UK "plotting the violent overthrow of foreign governments" including those of Libya, Iraq and Iran.
The file, now at the National Archives in Kew, also reveals that in October 1985 immigration facilities at Heathrow came close to being overwhelmed by an unexpected surge of young men from Bangladesh seeking entry to the UK.
It shows that a little-known scheme to pay immigrants who wanted to return to their country of origin - used by 100 or 200 people a year - had been rebranded "assisted return" because its original name, "voluntary repatriation", had sounded too like the kind of repatriation called for by Enoch Powell.
And it reveals that at one stage the home secretary of the day, Douglas Hurd, even contemplated breaking the law over the issue of polygamous wives.
In March 1986 he wrote arguing for a change in the law to make it possible to refuse such women entry.
"There is no way in which the issue of entry clearance applications by polygamous wives can be made acceptable to public - or Parliamentary - opinion," he wrote.
Until the law changed he was prepared to "postpone compliance with his legal obligation" to admit second wives, he said.
The attorney-general Sir Michael Havers soon put a stop to that, writing: "Such unlawful action by the government cannot be contemplated."
But in pressing for the change Mr Hurd - who called the admission of polygamous wives "a mischief" - had the prime minister on his side.
A note from one of her advisers says she "strongly shares the Home Secretary's view that an early change in the law is required".
When Mr Hurd suggested making future polygamous marriages invalid but recognising existing ones, she wrote in the margin: "We do not recognise polygamy at all."
And on the very last document in the file - a memo from the Foreign Secretary Geoffrey Howe outlining the difficulties involved in changing the law - she wrote, with multiple underlinings: "The country would be with us on this.
"We are crazy to discriminate in favour of the coloured Commonwealth against the UK."