It was supposed to begin running on route 38, between Victoria Station and Hackney, on February 20.
This isn’t the first setback for the long awaited bus – it was stranded on the M1 when it ran out of fuel on its way to its official unveiling.
It was also due to begin service last year, but it was rescheduled for Monday.
Disabled activists have also said that they don’t like the vehicle’s layout.
The bus cost Transport for London £11.37m to develop, which has also caused concerns.
Others have said the buses will encourage fare dodging – a problem that is costing over £30 million a year.
But the reception from Londoners when the bus was unveiled was mainly positive.
The new bus service is now due to begin on February 27.
Mike Weston, operations director for London Buses, said: “The first new bus for London is set to enter full passenger service next week. The vehicle is currently taking part in final road tests.
“We originally hoped that the first bus would start taking passengers from this week, but this has been slightly delayed as a result of the certification process required for new vehicles taking a little longer than anticipated.”
The bus needs to pass tests for emissions, steering, braking, seat fixtures, lights and alarm systems before it can get a new vehicle certificate from the Department for Transport.
The other seven Routemaster bus prototypes will begin service in the summer.
London Assembly Lib-Dem group and transport committee leader Caroline Pidgeon slammed the delay.
She said: “We were promised that the new Routemaster bus would be up and running in 2011, but the harsh reality is that just one of these incredibly expensive buses will be on our roads before this summer.
“This latest admission exposes once and for all Boris Johnson’s real record on bus services. He promised to deliver a new bus for London within his four-year term.
“In reality his record has been to hike up bus fares by 50 per cent and to allow buses to become more crowded.”