The Irish Guards' regimental mascot, Conmeal the Irish wolfhound, was given his own sprig of shamrock by the Duchess of Cambridge.
The St Patrick's Day tradition dates back to 1901.
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Celebrations to mark St George's Day have started in Trafalgar Square with feasts and tea to be found in abundance.
People took to the streets of Brixton today to march against what they see as the 'gentrification' of the area.