UK ministers were warned in July 2002 that Britain was committed to taking part in an American-led invasion of Iraq and they had no choice but to find a way of making it legal.
The warning, in a leaked Cabinet Office briefing paper, said Tony Blair had already agreed to back military action to get rid of Saddam Hussein at a summit at the Texas ranch of President George W Bush three months earlier.
The briefing paper, for participants at a meeting of Blairs inner circle on July 23, 2002, said that since regime change was illegal it was necessary to create the conditions which would make it legal.
This was required because, even if ministers decided Britain should not take part in an invasion, the American military would be using British bases. This would automatically make Britain complicit in any illegal US action.
US plans assume, as a minimum, the use of British bases in Cyprus and Diego Garcia, the briefing paper warned. This meant that issues of legality would arise virtually whatever option ministers choose with regard to UK participation.