Nearly four million eligible voters are still not on the electoral register, according to a new report.

The Electoral Commission, which carried out the research, said the voting registration system needs modernising if this figure, representing between eight and nine per cent of the eligible population, is to be reduced.

It is the first time in over a decade that an official count of voter registration numbers in England and Wales has been published.

The report, which draws on figures from the 2001 general election, found that over half of all non-registered people came from just three groups - those living with parents, home movers and private renters.

Non-registration was highest in densely populated urban areas with mobile populations, particularly inner London, and areas of economic deprivation.

And unsurprisingly, the youngest age groups are most likely not to be on the electoral register, with an estimated 16 per cent of 18 to 24 year-olds-not registered.

The report highlighted the current reliance on the head of the household to complete a form on behalf of others as a problem that can lead to whole families failing to register.

It says household registration is "outdated, open to abuse and error" and a new system of individual registration is urgently needed.

Sam Younger, chairman of the Electoral Commission, said new laws governing voter registration could bring the much needed changes.

"We look forward to the introduction of the Electoral Administration Bill, which we hope will include our recommendations for reforming the electoral system, most importantly reform of the system of voter registration," he said.

"Registration should be a matter for each individual rather than for heads of household and it is vital that a system of individual registration is introduced as soon as possible so that the register used at the next general election is secure, accurate and commands confidence."

The Conservatives backed the calls for urgent reform of the system.

Shadow constitutional affairs secretary Oliver Heald said: "The government's obsession with electoral 'modernisation' has compromised Britain's traditional reputation for free and fair elections, and undermined both the integrity of the system and public confidence in it.

"Ministers have not gone far enough to safeguard our democracy, such as by blocking individual registration and endorsing the future use of all-postal voting.

"Mainland Britain urgently requires the tried and tested Northern Ireland system of electoral registration, with the use of national insurance numbers to verify that those on the electoral roll actually exist."