Police say the man was arrested following a stop and search as part of an ongoing operation.

He is being detained under the Terrorism Act and is in custody in a south London police station.

"Detectives from the Counter Terrorism Command are continuing their investigation, and as a result of this arrest there is no immediate known threat," said the Met Police.

Police say a man has been arrested at Whitehall on suspicion of the "commission, preparation and instigation of acts of terrorism".

The man, aged in his late twenties, was also arrested on suspicion of possession of an offensive weapon, said the Met Police.

This photo is an aerial shot which appears to show a forensic officer crouching beside a brown backpack at the scene of the incident at Whitehall.

More pictures from the scene at Whitehall where a man has been arrested close to Parliament.

Image source, PA

Police have closed the main gate to Parliament following the incident at Whitehall.

Security has remained tight outside Whitehall buildings following the terror attack on Westminster Bridge and the entrance to Parliament on 22 March.  

This is the scene at Whitehall, where police say an arrest has been made following an incident. 

One witness has told the BBC two knives could be seen on the ground.

Image source, PA

Liberal Democrat leader Tim Farron has criticised Labour's handling of Brexit, describing that party as the "worst opposition in human history". 

"It is wrong to impose on Britain however they voted, whichever way they voted last June, an exit from the European Union without the final deal being put to them and of course in that vote on the final deal we would allow the British people a chance to vote for remaining if they wanted to. 

"What has a government got to be afraid of democracy? Talking about democracy, there is nothing more dangerous to a democracy than a government with an enormous majority and an appalling opposition."

Jeremy Corbyn says pledge is aimed at removing "sense of insecurity" among young people.

Armed police are at the scene of an incident in Whitehall. 

According to the BBC's Danny Shaw, a witness said he could see two knives on the ground - one a large bread knife. 

Scotland Yard said no-one has been injured and an arrest has been made. Police will be making a statement later. 

News from Boris Johnson's constituency of Uxbridge.

Political editor for BBC News London, Tim Donovan, tweets UKIP will not field a candidate against the foreign secretary.

Adam Holloway, Conservative MP for Gravesham, has thrown his support behind Foreign Secretary Boris Johnson following his comments about the UK potentially taking military action in Syria.

Mr Holloway told the BBC: "Some people try to present Boris as if he's some kind of joke. Boris Johnson realises you've got to have a political settlement in Syria. 

"The last thing you can have is the collapse of that regime, because all of the territory that we call Syria will be unimaginable chaos for yet more millions of people in the Middle East. He's no fool."

The World at One
BBC Radio 4

What kind of deal are we going to get for Brexit?

EU leaders are meeting this weekend to adopt their joint negotiating position on Brexit and there are signs that they could be toughening their stance. 

German Chancellor Angela Merkel has warned that some in Britain appeared to have illusions about the kind of deal they are likely to get. 

Conservative MP Dominic Raab was a leading campaigner for Brexit, and sits on parliament's Exiting the EU committee. 

He says the Brexit talks will be a "political haggling process" and "a two-way negotiation" and insists the UK "is not going to be paying a fee to leave the EU".  

Image source, PA

It wouldn't be an election campaign if we didn't see a photo of a politician holding a child.

Jeremy Corbyn held one-year-old Angelo after speaking to supporters at a rally in Harlow, Essex earlier today.

Image source, University of Reading

Ex-UKIP MP Douglas Carswell has been putting the boot into his old party again.

He claims the party's chances at the general election are "pretty bleak".

The Clacton MP, who began his political journey as a Tory MP quit UKIP in March and is now retiring from politics altogether. 

Speaking at a Political Voices talk at the University of Reading, he said: "One reason why many people in UKIP are no longer running is because they’ve finally learned at the end of their political career what you should learn at the start…. is how to count. The maths on the wall are pretty bleak for UKIP.”

Image source, Twitter/@jpjanson

The word mugwump has been doing the rounds on social media today after Boris Johnson used it to refer to Labour leader Jeremy Corbyn.

Many people are speculating whether the term is an insult or a compliment by sharing all the mugwump memes and references they can think of.  

Read our full story on how mugwump has taken over social media.

Ellie Price
Daily and Sunday Politics reporter

Image source, Reuters

The BBC's diplomatic correspondent, James Landale, says that sometimes in diplomacy it matters if politicians say things publicly into a microphone.

And we now have it on the record from Foreign Secretary Boris Johnson that the UK is willing in principle to attack Syrian government targets at the behest of the United States.

And this is not just Mr Johnson's view, our correspondent adds - he said it was the prime minister's view too.

You can read more from James Landale on this here.