David Cameron urges Londoners to go out to pubs and offices and say No

David Cameron has called on Londoners to press the case against voting reform in homes, pubs and offices across the capital.

Writing exclusively for the Standard, the Prime Minister said next month's referendum was vital for the future of Britain's democracy and warned of the dangers of a low turnout.

He said: "The biggest danger right now is that not enough people turn out to vote and Britain sleepwalks into this second-rate system, waking up on May 6 with a voting system that damages our democracy permanently.

"In many ways, your vote alone is not enough. In the days and weeks ahead, you also need to challenge your friends and colleagues who are thinking of voting 'yes'. Ask them why they are voting for it. I bet you none of their arguments will stack up - and you need to take them on."

Mr Cameron argued that first-past-the-post was "clear, simple and decisive" and allowed voters to kick out "dog-tired" governments.

He warned AV would make it harder to reject "dead" administrations and would make coalitions more likely, risking a "litter of broken promises".

Experts have warned that turnout in the capital could be as low as 15 per cent for the referendum on changing the way Britain elects its MPs because no local elections are being held, as they are in the rest of the country.