EU helps protect UK energy supply from Russia's Putin, says pro-EU minister

(Adds reaction)

LONDON, March 24 (Reuters) - Britain's membership of the European Union helps secure the country's energy supply from any possible threat by Vladimir Putin's Russia to restrict gas flows, energy minister Amber Rudd will say on Thursday.

Her comments are part of the government's campaign to persuade Britons to vote to stay inside the EU at a June 23 referendum and were immediately criticised by rival campaigners who want to leave the bloc as scaremongering.

Public opinion is evenly divided and many voters are undecided on an issue that will define the country's future global role.

Rudd will argue in a speech that Britain's dependence on imported gas is "not without risk" and that EU membership gives it greater negotiating power in supply disputes.

Russia provides around 30 percent of the EU's gas and a single supply deal signed last year by Britain's biggest energy supplier Centrica (LSE: CNA.L - news) meant that at the time Russia's Gazprom would meet 9 percent of the country's gas needs.

"We have seen how countries such as Putin's Russia use their gas supplies as a tool of foreign policy, threatening to cut off supplies or drastically increase prices," Rudd will say according to advance extracts of her speech.

The proportion of domestically produced gas used in Britain is expected to fall to 26 percent in 2030, down from 56 percent last year.

"We can't let our energy security be hijacked as a political pawn to bring Europe to its knees. By working together in the European Union, each member state can stop this becoming a reality ... To put it plainly - when it comes to Russian gas, united we stand, divided we fall," she will say.

She (Munich: SOQ.MU - news) will also say that an exit from the 28-member EU would threaten foreign investment in Britain's energy industry.

Rudd's argument was criticised as scaremongering by one of the main 'out' campaigns - a familiar charge in what is becoming an increasingly bitter debate.

"Putin does not have the power to switch off the lights in Britain, as the Energy Secretary implies. In any case, we can't decide our nation's future based on whether we think Putin will smile or frown," said Alex Deane, executive director of the Grassroots Out Movement. (Reporting by William James; editing by Stephen Addison/Elizabeth Piper)