It's true, but it's a 'canard'...

Of course she got a significant amount of votes - but it just is not true to call that 'a majority', and it should never be allowed to stand. As you say, MtheGM, it is unheard of for a single party to get a majority (the nearest party to doing that was Labour in 1951 - and under the British electoral system it lost the election to the Tories, who got less.

To suggest that Margaret Thatcher managed to achieve that is to claim she achieved a much more impressive victory than she actually did, as it would be to claim that most voters backed Tony Blair.