David Cameron will urge the public to take a "once in a generation chance" for democratic reform today by backing city mayors.

Voting yes in referendums a week on Thursday will give areas powerful champions to represent their interests, according to the prime minister.

Speaking to Tory activists in Bristol, Cameron is to say: "Britain stands on the brink of exciting democratic change.

"Let's be clear what this moment means. It's not some trivial re-structure or fiddling about.

"It's about more investment across our country. More jobs for our workers.

"More life in our political system. It's a once-in-a-generation chance to change the way our country is run.

"I passionately want those cities - from Bristol to Birmingham, Nottingham to Newcastle, Sheffield to Wakefield, to give a resounding, emphatic yes next week."

Cameron warned that cities risked "stagnating" if mayors were not introduced.

"If you want your local champion speaking to the heart of Government, banging their fist on the table for Birmingham, or Bristol or Leeds - get out and vote yes," he said.

"If you want to see your city grow more prominent, more powerful, more prosperous - get out and vote yes.

"This is a once-in-a-generation chance to change the way we run our country, so seize it, vote for it, go for it."

A series of high-profile Labour MPs have expressed their interest in running for Mayor.

Liam Byrne recently announced his departure from the Shadow Cabinet in order to run for Mayor of Birmingham. He is set to face other Labour candidates, including Gisela Stuart and Sion Simon.

While former Labour defence secretary Bob Ainsworth has been lined up to be Mayor of Coventry.

This comes amid suggestions that Labour HQ may prevent MPs from standing if they resign their seats in order to run for mayor.