She has no vote in Britain, but German Chancellor Angela Merkel could be key to Prime Minister David Cameron's re-election hopes.

The German leader is in London for talks, and Cameron is hoping she'll support his plan to keep the U.K. within a reformed European Union.

With anti-EU sentiment rising, Cameron has promised a membership referendum if he wins May's election. He wants Britain to stay in the EU, but needs reforms to sell the idea to his Conservative party, and to voters.

Cameron wants Merkel's support for a plan to impose limits on movement of people within the 28-nation bloc.

Merkel, who broadly shares Cameron's center-right economic stance, has indicated she may support restrictions on benefits for migrants, but has insisted the free movement of workers is non-negotiable.