David Cameron stressed the need to "hunt down the traffickers who prey on human misery" as he hailed an emerging agreement among European leaders over the Mediterranean migrant crisis.

Following emergency talks in Brussels, the Prime Minister said there was a consensus building on a "comprehensive strategy" as he announced the deployment of Britain's biggest warships to the region.

"What's emerging is what we need which is a comprehensive plan, going after the criminal gangs, going after the traffickers, going after the owners of the boats - potentially taking action there as well and stabilising the countries from which these people are coming," he said.

Writing in the Daily Mail, Mr Cameron admitted there was a need for more search and rescue missions, calling the deaths of 800 migrants travelling in a boat which capsized last weekend "absolutely shocking".

"Eight hundred people died in the most horrific of circumstances, so it's also right that Britain - not just a compassionate country but a strong one too - does what it can to prevent such scenes ever happening again," he said.

"We need to hunt down the traffickers who prey on human misery, deal with the boats that bring people across the seas and help foster stable conditions in countries which export so much illegal immigration.

"Only then will we properly get to grips with this situation - building confidence at home that people can't come here illegally; and helping people abroad live safe and secure lives."

Earlier he announced that he would be sending the Navy's flagship, HMS Bulwark, to join an enhanced search and rescue mission in the Mediterranean. But he insisted there was no question of Britain offering asylum to the migrants it plucked from the sea.

"I think it's right for Britain to step forward, for the Royal Navy to play a role. They will be saving lives not offering asylum in the UK," he said.

"That's the role we can play in the immediate term but a comprehensive strategy is what in the end will make the difference and solve this problem."

European Council president Donald Tusk said the meeting had agreed a four-point plan to tackle the issue including measures to take out the boats used by the people smugglers before they take to sea.

Mr Tusk said: "Europe did not cause this tragedy, but that doesn't mean we can be indifferent. We are facing a difficult summer and we need to be ready to act."

Britain's contribution led by HMS Bulwark will be supported by two UK Border Force cutters and three Royal Navy Merlin helicopters with sophisticated radar designed to spot small surface vessels over long distances.

The 19,500 tonne assault ship - currently in the Dardanelles for the Gallipoli centenary commemorations in Turkey - will be on the scene ready to start search and rescue operations within the week.

It will extend well beyond the range of the current EU Operation Triton, which is restricted to Italian coastal waters and controversially replaced the more extensive Italian navy Operation Mare Nostrum last year.

It will also provide a floating refuelling platform for the Merlins - expected to be based in either Malta or Sicily - enabling them to extend the range of their patrols.

Bulwark is expected to continue operations for around two months after which Britain is hoping that other member states will take up the reins.

The Prime Minister was adamant that the operation to save lives did not mean Britain would offer asylum to the people it rescued, insisting that they must be dealt with in the nearest safe country to where they are picked up.

He stressed however that Britain's involvement depended upon the "right conditions" being in place.

"That must include that the people we pick up and the people we deal with are taken to the nearest safe country - most likely Italy - and don't have immediate recourse to claim asylum in the UK," he said.

With more than 1,700 migrants feared drowned already this year, the Refugee Council said the measures agreed in Brussels would not help those currently at risk making the perilous crossing in overcrowded and unseaworthy vessels.

Chief executive Maurice Wren said the refusal of countries like Britain to offer asylum to the refugees was effectively slamming the door in their faces.

He said: "Patrolling the Mediterranean and smashing the smugglers may sound like the priority, but what will become of those who are fleeing for their lives right now if we aren't prepared to provide them with alternative routes to safety? What's the use of stopping people drowning on our doorstep just to watch them being beheaded, butchered or shot in northern Africa?

"The UK government speaks about our proud tradition of protecting refugees, yet when the Syrians and Eritreans come knocking on the door of Europe begging to be protected, we slam it in their faces."

Shadow home secretary Yvette Cooper said: "The commitment from Europe to increase resources and action to tackle the humanitarian crisis in the Mediterranean is welcome. European governments were wrong to drop search and rescue last year, and wrong to argue - as the British government did - that this was justified to deter others from travelling too.

"So it is extremely important that Europe has promised to increase the mission at sea. Anything short of a properly resourced and extensive search and rescue mission will be a moral failure. Additional vessels and resources are welcome, as is action from Europol to tackle the criminal traffickers.

"But a long-term and comprehensive strategy will be needed to deal with the ongoing crisis. And ahead of the Council in June the world will be watching to ensure the decisions taken today result in real humanitarian change."

Steven Woolfe, Ukip's migration spokesman, said Britain had a responsibility to take some of the refugees.

He told BBC Radio 4's Today programme: "Nigel has said that we should do so.

"Nigel actually said this when the Syrian crisis started some time ago.

"We must get some people yes, I think that's clear."

But he added that while many of those risking the journey across the Mediterranean are fleeing desperate situations, some are economic migrants.

Dr Kandeh Yumkella, United Nations undersecretary-general, said Europe and other countries should be doing more to deal with the "long-term push factors" that are drawing people to take the "miserable journey".

The Sierra Leonean economist told BBC Radio 4's Today programme: "The immediate term efforts for humanitarian assistance dealing with the smugglers are correct, but we should look at the long-term.

"So far this year, it's about 35,000 people that have tried to cross.

"But remember, if you take the African context, you have a billion people now, another billion will be added in 35 years.

"Those numbers of people trying to cross will be larger if you don't have better economic possibilities and opportunities in the south, in Africa.

"I think beyond a 'fortress Europe' approach, we should be looking at a 'prosper thy neighbour' approach.

"Which means we push wealth creation in African countries, we push investments in energy access and infrastructure that will open up these economies and create wealth to reduce the urge to move."