It is quite possible that Minister Thatcher was using what is called an 'Empirical We'. This would be common for leaders in England, and would explain the grammar. It was common for the king, Emperor, or other ruler to refer to themselves always in the plural. This stems from two different etymologies. One was that they were considered ordained of God, and so were never acting alone. The other is that in most Latin-derived languages, the plural form is the more formal.
The cause of the uproar following this comment was that it is the Queen that uses the Royal 'We'. Thatcher's use of the word suggested to some that she had delusions of grandeur. I seem to recall, in fact, Thatcher also referred to herself as the Head of State, which again is the Queen.
(Casey Alderbran - UK)
Maggie kept using the 'Royal we' throughout the last years of her reign/dictatorship. Its not as good as the (probably apocryphal) story when she was touring the country after becoming a baroness and she was visiting an old peoples home and said to one of the ladies:
"do you know who I am?"
"no dear, but matron can tell you"
This was a comment which led to a remark by Neil Kinnock (leader of the opposition at the time) that the (then) new £1 coin should be called a Thatcher -- "Because it's thick, brassy and thinks it's a sovereign".