LONDON (Reuters) - Britain is investing in extra patrol boats and surveillance to try to prevent migrants crossing the English Channel, a spokesman for Prime Minister David Cameron said on Tuesday.

Cargo ships are seen as they sail across the English Channel with the French coast on the horizon, from Dover in Britain, January 9, 2016. REUTERS/Toby Melville/File Photo

Twenty people, including 18 Albanians, were rescued from the Channel over the weekend after their inflatable boat started taking on water.

Last year, extra fencing, cameras and police were deployed at the French terminal of the channel tunnel after passenger and freight services were severely delayed by migrants trying to stow away to Britain.

“We have taken measures at Calais which have improved the situation there: it is clear that people are now trying different routes and we will look to cut those off,” Cameron’s spokesman said.

“We take every necessary action to protect our border security and will continue to do so.”

The government has said the Border Force, which currently has three vessels, will get extra patrol boats to help tackle smuggling of weapons, drugs and migrants. The first batch will be in place in the coming months, it said, but declined to specify how many boats that would include.

Border Force officers have been given extra powers to stop, board, divert and detain vessels and make arrests, and three maritime hubs will also be set up to improve intelligence.

“Our intent is to prevent people attempting to cross the Channel ... we are taking steps to improve our ability to combat them,” the spokesman said.

Immigration is a key part of the debate over Britain’s European Union membership ahead of a June 23 referendum.

A poll published in Tuesday’s Daily Telegraph newspaper showed support for leaving the EU had grown by 4 points to 46 percent, with Cameron’s former political strategist Lynton Crosby attributing the boost to the “Out” campaign’s focus on migration over the last seven days.