The cost of the project, which began in June of last year, has also over-stretched by around £3m.

Motorists can now expect long delays on the motorway over the busy Christmas period and into the new year.

Contractors have blamed the wet weather for the delay.

Work is being carried out to replace worn out carriageways around Spaghetti Junction as well as strengthening beams underneath the motorway.

'Exceptional weather'

Roadworks were originally scheduled to last 16 months and should have finished by Christmas.

Contractors say a major part of the work involves waterproofing which can't be done if it's raining.

Geoff Bethel, of the Highways Agency, said: "We started this phase of the water proofing in the middle of October and since then we have had only six days when it hasn't rained all the way through October and November.

"We obviously allow for weather. We know we need to take account of weather at this time of year.

"We have done that and there was a very generous allowance within the contract to allow for that but this has just been exceptional."

The Highways Agency has pledged to minimise any disruption over the Christmas period but drivers are being warned to expect congestion.