Mr Brown posed with his wife, Sarah, and volunteer poppy collectors on the steps of 10 Downing Street this morning.

Three of the volunteers were wearing yellow Stand With Me” T-shirts, echoing the message of the campaign.

Forces sweethearts Dame Vera Lynn and Hayley Westenra will launch the official campaign on Thursday at Horseguards Parade in central London, a Royal British Legion spokesman said.

He said: “The Prime Minister was presented his poppy this morning, as is the tradition, in advance of the launch of the poppy appeal.”