The authorities have narrowly avoided the M4 becoming a “national embarrassment”, by reopening the motorway to cars today in time for the start of the Olympics build-up this weekend.

Labour declared this week that the continuing closure of the M4 between junction 2 and 3, with just over a fortnight until the start of the Olympic Games, threatened the UK’s national standing.

It came after the Highways Agency (HA) missed its self-set target of reopening the M4 to traffic yesterday. The motorway had been closed since last weekend when a crack was found within the fabric of the Boston Manor Viaduct during scheduled repair work.

In a statement issued today HA says: “an exceptionally delicate and difficult operation to repair cracks in the Boston Manor Viaduct on the M4 has been successful”.

Transport for London (TfL), which is managing the Olympic Route Network for the Games, has been warning motorists to avoid central London from this weekend (14-15 July). Officials and athletes are expected to begin arriving in the capital en masse ahead of the start of the competition on 27 July.

TfL will now be able to switch on the M4 Games Lane (the old bus lane) from 15 July to speed the Olympic family on their way, helping mitigate the extra congestion.

A ban on vehicles of 7.5 tonnes and over remains in place between junctions 2 and 3 of the M4. A spokeswoman for the HA says access for LGVs will be restored in the future, although as yet there is no date as to when this will occur.