Baroness Thatcher's funeral procession is under way in central London in what David Cameron has called a "fitting tribute to a great prime minister".

Crowds applauded as her union jack-draped coffin began its journey from Westminster to St Paul's Cathedral for the funeral.

Four thousand police are on duty but there were no signs of protests.

Some 2,300 people, from 170 countries, are expected to attend. The Queen will be among them.

The hearse was flanked by police outriders as it left Parliament, where her body lay overnight, to travel to St Clement Danes, the RAF church on The Strand.

As it arrived, the coffin was taken into the church, ready to be transferred to a gun carriage to be taken to St Paul's.

A white floral arrangement on top of the funeral bore a card reading: "Beloved mother, always in our hearts."

Prayers were said by St Clement Danes' resident chaplain the Rev David Osborn.

'Sombre event'

Lady Thatcher, who was Conservative Prime Minister from 1979 until 1990, died on 8 April, following a stroke, at the age of 87.

She has been accorded a ceremonial funeral with military honours, one step down from a state funeral.

Speaking on BBC Radio 4's Today programme, Mr Cameron said it would have been seen as extraordinary not to commemorate her life.

"I think it will be quite a sombre event, but it is a fitting tribute to a great prime minister respected around the world, and I think other countries in the world would think Britain had got it completely wrong if we didn't mark this in a proper way,"

Asked about those who wanted to challenge his view of Lady Thatcher, the prime minister said: "Of course people have the right to disagree and take a different view.

"But when you're mourning the passing of an 87-year-old woman who was the first woman prime minister, who served for longer in the job than anyone for 150 years I think it's appropriate to show respect."

He said he had been "partly" inspired, as a young man, to join the Conservative Party by Baroness Thatcher, who he thought was a "very brave woman doing a tough job". (BBC)