Coat of arms of Margaret Thatcher, The Baroness Thatcher (1925-2013), Prime Minister of the United Kingdom from 1979 to 1990. Granted originally by the College of Arms in 1992 and was designed by the Garter King of Arms Sir Colin Cole.
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On a lozenge per chevron azure and gules, a double key in chief between two lions combatant a tower with portcullis in base all or

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The key and the two royal lions of England represents her tenure as Prime Minister and First Lord of the Treasury. The tower and portcullis represents her time at the Palace of Westminster as Member of Parliament. She bears this achievement on a lozenge (as is traditional for a woman).
Own work, Based on the heraldic blazon and other works: [1] [2]
Sodacan