Mrs Thatcher's funeral is about to start. Watch the live BBC coverage of the ceremony here:
BBC News - LIVE: Baroness Thatcher funeral
Her coffin will leave the Palace of Westminster at 10:00am, about 15 minutes from now, before being transferred to a gun carriage at the RAF's Church of St Clement Danes, then processing to St Paul's Cathedral.
The route will be lined by members of the armed forces.
The mourners will be led by the Queen and Duke of Edinburgh. The congregation includes two heads of state and 11 serving prime ministers.
Some 2,300 people are expected to attend the funeral. Around 4,000 police officers are on duty in central London
For the first time since the funeral of Sir Winston Churchill in 1965 the bells of Big Ben have been silenced.
Sarah Ferguson, Duchess of York, is one of the guests who has arrived for the ceremony.
Some 2,300 people are expected to attend the funeral. Around 4,000 police officers are on duty in central London.
Guests have started to take up their seats at St Paul's Cathedral.
tweets: Falklands veterans at Ludgate Circus waiting for funeral procession.
There is a loud cheer as pensioners of the Royal Hospital Chelsea arrive by bus. They will later form a Guard of Honour on the steps of St Paul's when Baroness Thatcher's coffin arrives. The group of 16 brighten up an otherwise rather damp and overcast day.
Security is tight in central London ahead of the funeral. In the last 24 hours, hundreds of police officers have patrolled the streets with sniffer dogs trained to detect explosives.
One lady who has a fascinating story to tell is Sue Bloxham, 70, from Norfolk.
She was a 20-year-old City of London policewoman during Winston Churchill's funeral in 1965.
"I was standing just a few yards away from this point," she says, pointing from her spot in front of two red phone boxes directly opposite St Paul's.
"It feels strange, I feel almost wobbly," she says.
"There's not the same patriotism that there was for him. We were there united in supporting him.
There's one or two people round here today who are not being very respectful."
Some have travelled many more miles to be here.
Margaret Kittle, 79, who travelled to London from Winona, Canada, for the funeral, says she has been in position since Tuesday morning.
As camping is not allowed in the City since the Occupy protests she has made do with a fold-up chair and warm clothes.
"I'm a great admirer of Mrs Thatcher. I was here each time she won [general] elections," she says, standing behind the flag of her country.
"She took on Gorbachev and Reagan and liberated people from the iron curtain, she kept the Falklands in British control and took on the unions. She was a strong woman. She made Britain great again."
She says her family were at Churchill's funeral and says of Thatcher's: "It will be sad - it's the end of an era in politics."
A group of undertakers, whose firm was founded in 1789, has just put Mrs T's coffin into the hearse.
The crowds lining the streets seem to be larger than some people expected.
Mayor of London Boris Johnson told Sky News outside St Paul's: "Even for her fans and supporters like me, I don't think we expected to see quite so many people turn up to show their affection and their respect for Margaret Thatcher. It is a quite astonishing crowd."
The BBC's Home Affairs Correspondent Dominic Casciani says he has just heard the day's first protest at Ludgate Circus.
"As a military band marched up Fleet Street in all its pomp, one side of the crowd clapped them enthusiastically - but the other side booed loudly.
"Protesters chanted 'waste of money' as the band marched past."
But there aren't as many protests as some thought there would be.
At St Clement Danes, the BBC's Lesley Ashmall is watching the coffin being taken from the hearse.
"The crowd is really silent now, with very few dissenting voices, I've seen two placards.
"The bells of St Clement Danes are tolling as the body of the former prime minister is taken into the chapel."
Prayers are being said by St Clement Danes resident chaplain the Reverend David Osborn as the coffin, draped in a Union flag, is transferred to a gun carriage of the King's Troop Royal Horse Artillery for the military procession to St Paul's Cathedral.
This is the pomp and ceremony which brings tourists to London.
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