The next London elections are to be conducted under a system so complex that using computers to count the votes is the only viable way of deciding what the outcome is.

It was announced on Tuesday that Milton Keynes-based company Data and Research Services had been awarded the £3.5 million contract to oversee the electronic counting of votes.

Elections for the capital's mayor and to the London assembly will be held on June 10 next year, and will be combined with those for the European parliament.

Londoners will have a total of five votes, including a first choice and a second choice for mayor.

They will also have a vote for a constituency assembly member and one for a London-wide assembly member chosen by voting for a political party or an independent candidate.

And the fifth vote will be for a designated political party or independent candidate, which will form a London-wide list of MEPs.

The result for the mayoral elections will be calculated using the supplementary vote system.

The London assembly is calculated using a combination of first-past-the-post for constituency members and the additional member system for London-wide members.

And the European parliament is elected using the party list system.

Anthony Mayer, the Greater London returning officer, said that combining the London mayoral and assembly elections with the European parliamentary elections "will create one of the largest and most complex polls ever held in the UK".

There will be fears, however, that the hugely complicated system could dent voter turnout and prompt confusion about how to cast votes.

But DRS said it was confident of being able to deliver accurate results.

The electronic counting contract will see the firm delivering electronic counting technology for the entire London mayoral and assembly ballot.

The company will also design and print the ballot papers, supply ballot boxes, counting machines and on-site technical support for the constituency count centres across London.

Ballot papers will be scanned through specially-designed machines that capture and store the information on a secure database.

"With exactly one year to go, DRS are delighted to be working on the London Mayoral and Assembly elections. We are confident that we can deliver the election results securely, accurately and efficiently," said DRS managing director Tony Lee.

The automated counting process means that multiple votes and different voting systems can be calculated at the same time.

It is expected that "e-counting" will enable the entire count to be completed many times faster than if it were done manually, given that over seven million individual votes were cast in 2000.