A day of political campaigning took a dramatic twist, as the Prime Minister and Boris Johnson helped a woman after seeing her lying in the street.

The pair were on their way to a campaign event when the Mayor of London saw a woman, believed to be in her 20s, who had collapsed in the middle of Sheepcote Road, Harrow.

Watch: Prime Minister David Cameron joins Mayor of London Boris Johnson at Harrow College

David Cameron's security team then called 999, with the political heavyweights staying with the woman until the ambulance arrived.

When Dominic Stark, one of the paramedics who attended the scene, arrived after getting the call at 11.19am, he was shocked to see David Cameron holding the woman's hand.

He said: “I was told the Prime Minister and Boris Johnson had pulled over when they noticed a woman collapsed on the street.

“When I arrived a few minutes later, I found the PM holding the woman’s hand. I took over caring for the patient and they left a few minutes later.”

The patient was then taken to Northwick Park hospital.

A spokesman for the London Ambulance Service said: “We were called at 11.19am this morning to reports of a woman taken unwell on Sheepcote Road, Harrow.

“We sent a paramedic in a car, who arrived in three minutes, and an ambulance crew to the scene."