Parts of Britain are "under siege" from immigration, prompting the government to look at ways to stem the number of EU workers arriving, Defence Secretary Michael Fallon said Sunday.

"In some areas of the UK, down the east coast, towns do feel under siege, (with) large numbers of migrant workers and people claiming benefits," Fallon told the BBC.

"We are looking at changing that to make sure there is some control. We are fully entitled to say this is making a difference to us, that now needs to be dealt with."

Fallon said London was determined to push ahead with immigration reforms, despite a blunt warning on Saturday from German Chancellor Angela Merkel that any attempts to "tamper with the fundamental principles of free movement in the EU" would not be tolerated by Britain's European partners.

"The Germans haven't seen our proposals yet and we haven't seen our proposals yet, and that's still being worked on at the moment to see what we can do to prevent whole towns and communities being swamped by huge numbers of migrants," Fallon said.

British Prime Minister David Cameron's Conservative Party is aiming to curb immigration, as it faces increased electoral pressure from the anti-EU UK Independence Party.

Unless the prime minister can woo back right-wing voters tempted by UKIP's hardline rhetoric, party faithful fear that they will lose next year's general election to the Labour Party.

Under EU rules, citizens of most EU countries have the right to live and work in any other EU country.

Cameron has vowed to offer Britons a referendum by 2017 on whether to stay in the EU or not, if his party wins the 2015 election.