David Cameron sparked a major political row today after describing hundreds of migrants in Calais as a 'swarm'.

Labour's acting leader Harriet Harman said the Prime Minister should remember he is talking about 'people, not insects' as tensions mounted over the government's response to the crisis.

But political opponents accused him of 'dog-whistle' politics and the Refugee Council condemned the 'awful, dehumanising language'.

Prime Minister David Cameron blamed the crisis in Calais on a 'swarm of people coming across the Mediterranean, seeking a better life, wanting to come to Britain'

The row erupted after Mr Cameron sought to insist the government was taking action to deal with the crisis in Calais.

Speaking in Vietnam during his south-east Asian tour, the Prime Minister said the French had sent an extra 120 police and the UK was investing in fencing and security measures at the Channel crossings in Calais and Coquelles.

Mr Cameron told ITV News: 'This is very testing, I accept that, because you have got a swarm of people coming across the Mediterranean, seeking a better life, wanting to come to Britain because Britain has got jobs, it's got a growing economy, it's an incredible place to live.

'But we need to protect our borders by working hand in glove with our neighbours the French and that is exactly what we are doing.'

He should remember he is talking about people, not insects Acting Labour leader Harriet Harman

Acting Labour leader Harriet Harman said the Prime Minister appeared to want to whip people up against the migrants.

She told BBC News: 'He should remember he is talking about people, not insects.

'I think it's a very worrying turn that he appears to be wanting to be divisive and set people against, whip people up, against the migrants in Calais when what he should have been doing, and should have been doing months ago and was warned to be doing, is to get the situation sorted out with the French.'

Ms Harman dismissed calls for the British Army to be sent in to sort out the problem.

'I don't think there should be any question of us sending in our army. The French themselves have got troops as well as a large police force.'

Overwhelmed: A police officer watches helplessly as a group of migrants trying to reach the Channel Tunnel sprint past him

Gang mentality: The migrants are overwhelming police as they rush the Channel Tunnel in huge numbers as they desperately try to board trains knowing police are unlikely to chase them on the railway tracks

Labour leadership contender Andy Burnham wrote on Twitter: 'Cameron calling Calais migrants a 'swarm' is nothing short of disgraceful.

'Confirms there's no dog-whistle these Bullingdon Boys won't blow.'

The Refugee Council described Mr Cameron's remark as 'awful, dehumanising language from a world leader'.

The council's head of advocacy Lisa Doyle further added: 'It's extremely disappointing to hear the Prime Minister using such irresponsible, dehumanising language to describe the desperate men, women and children fleeing for their lives across the Mediterranean Sea.

'This sort of rhetoric is extremely inflammatory and comes at a time when the Government should be focused on working with its European counterparts to respond calmly and compassionately to this dreadful humanitarian crisis.'

The Joint Council for the Welfare of Immigrants (JCWI) said it was 'extremely concerned' by Mr Cameron's language.

'To refer to desperate human beings as a 'swarm' is demeaning and ignites the flames of xenophobia,' said the JCWI in a statement.

'Such 'tabloid style' language is unnecessary and demeaning. Any continued rhetoric on such a sensitive subject will undo decades of race relations work in the UK. It will also undermine our respect and standing in the world.'

Liberal Democrat leader Tim Farron said: 'By blaming 'migrant swarms' for the current crisis in Calais, David Cameron risks dehumanising some of the world's most desperate people. We are talking about human beings here, not insects.

'By using the Prime Minister's language, we lose sight of how desperate someone has to be to cling to the bottom of a lorry or train for the chance of a better life.'

Labour leadership contender Andy Burnham wrote on Twitter: 'Cameron calling Calais migrants a 'swarm' is nothing short of disgraceful.' Ukip leader Nigel Farage also tried to distance himself from the term, barely an hour after using it himself

Ukip leader Nigel Farage also tried to distance himself from the term, suggesting it was part of an effort by Mr Cameron to appear 'tough' on immigration.

Asked if he would use the word 'swarm', Mr Farage told BBC Radio 4's Today programme: 'No. No, I'm not seeking to use language like that.

'The Prime Minister is this morning trying to sound tough. Whether he actually means it or not is quite a separate question.'

But barely an hour earlier, Mr Farage had used the term himself, telling ITV's Good Morning Britain: 'A couple of times I've been stuck on the motorway surrounded by swarms of potential migrants to Britain.'

Meanwhile, the United Nations Secretary General's special representative on international migration, Peter Sutherland, said demands for economic migrants to be kept out of the UK are 'a xenophobic response to the issue of free movement'.

Mr Sutherland told BBC2's Victoria Derbyshire programme: 'In my opinion, the debate in the UK is grossly excessive in terms of Calais. We are talking here about a number of people - a relatively small number in the context of what other countries are having to do - who are in terrible conditions and have to be dealt with by France and/or Britain.'

The migrants crossing the Mediterranean by boat are 'in the main' genuine refugees fleeing violence and persecution, he said.

'Germany last year received 175,000 asylum applications. Britain received 24,000,' said Mr Sutherland.

'We are talking here about between 5,000 and 10,000 people in Calais who are living in terrible conditions. The first thing we have to do collectively is to deal with their conditions. Instead of talking about sending Gurkhas or building fences, we should be thinking of the humanitarian crisis.'

Mr Sutherland urged the UK to join the common European approach to the migrant issue, warning: 'Anybody who thinks that by erecting borders or fences in some way a particular state can be protected from alleged 'floods' - which are anything but floods - of migrants is living in cloud cuckoo land.'

After Mr Cameron was criticised for using the word, a Number 10 spokesman said: ‘If you look at the full sentence that the PM said it was clear that he was talking about people who are seeking a better life. It was clearly talking about people.

‘The point he was trying to convey was the tens of thousands that have been coming across the Mediterranean and into Europe and then seeking to come across to the UK, the scale.’

Asked if he regretted saying ‘swarm’, she said: ‘It was clear what he was talking about.’