Almost 20 per cent of signatures on a petition calling for a referendum for a directly elected mayor (DEM) in Plymouth are invalid.

Submitted by a campaign group called Yesdemplymouth campaign, people signing it have to be registered electors in the city and provide correct information to be counted.

Of 13,250 names on the petition, 2,394 have been excluded.

To be progress to a referendum, the petition 9,789 people needed to sign it,  five per cent of Plymouth’s electorate.

As 10,856 signatures were validated, the referendum must go ahead within six months.

Plymouth City Council has now published a notice of valid petition on its website.

The referendum will decide whether people want to elect a mayor or stick with the current arrangement where a council leader is chosen by councillors.

The poll has to be held by 6 August at a cost of £410,000.

If people agree they want a directly elected mayor, the vote is expected to be held in May next year.

Plymouth last rejected an elected mayor in 2001 when 59 per cent of people who took part voted against.

Both the Conservatives, who led the council at the time, and Labour campaigned for a ‘no’ vote and take the same view today.

Council leader Tudor Evans said the cost of running a mayor’s office would be in the region of £1.5 million a year, which would have to come out of money spent on services and the role would be similar to his, with no extra powers or money.

Leader of the Conservative group Cllr Andy Lugger believes it is “a bridge too far”  when the government wants ‘strategic authorities’ covering areas with more than 1.5 million people overseen by mayors.

But a spokesperson for the Yesdemplymouth campaign said the referendum is a “huge opportunity for Plymothians to shape a positive future."