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David Cameron has ruled out changing the date of a referendum on the Westminster voting system amid concerns the campaign could be totally obscured by the Royal Wedding a week earlier.

The referendum on how MPs are elected is set to be held on 5 May 2011, less than a week after Prince William's marriage to Kate Middleton on 29 April.

Mr Cameron denied the campaign would be drowned out by the royal spectacle.

He said people were "perfectly capable" of separating the two events.

Legislation paving the way for the referendum to be held on 5 May, the same day as devolved elections in Scotland, Wales and Northern Ireland, was approved by MPs earlier this month despite existing concerns about the date.

Nationalist parties have said the poll will distract from the key issues in their own campaigns while some Conservatives are concerned that voters in some parts of England - where no other elections are taking place - will have less incentive to vote and this could produce a distorted result.

The House of Lords is currently debating the bill but if it become law, the public will be asked whether they want to replace the current first-past-the-post system with the Alternative Vote (AV) model.

After royal officials announced the wedding would take place at Westminster Abbey on 29 April, Mr Cameron - who was consulted over the date - confirmed the day would be a public holiday in England, Wales and Northern Ireland. The Scottish government is expected to follow suit.

But he denied that the wedding date, coming ahead of the May Day bank holiday on 2 May, would mean the public would have very little interest in the referendum campaign in its final days.

"The timing of the wedding is entirely a matter for the Royal Family," Mr Cameron said.

"I actually think people are perfectly capable of seeing the difference between a Royal Wedding - a happy day, a day of celebration - and a referendum campaign and a local election campaign.

"I think people are quite capable of separating the two and I think it is quite right that the Royal Family should choose the day of their wedding."

Mr Cameron agreed to a referendum as a price of his coalition deal with the Liberal Democrats and deputy prime minister Nick Clegg has pressed for an early public vote on the issue.