Race is on for M4 repairs to avoid Olympic embarrassment

On Tuesday morning I visited the Boston Manor Viaduct after last week's crack appeared in the structure during routine repairs.

It led to the M4 being immediately shut and has caused all sorts of problems for commuters in west London.

Engineers were fixing plates over weld joints when a crack was discovered on Thursday, adjacent to the work they were doing.

When the engineers returned on Friday it had opened up further and it was shut extremely quickly.

Engineers feared a "catastrophic failure" of the structure.

I'm told these bridges do not sag when they fail, they simply collapse.

Even Transport for London (TfL) was only given 30 minutes' notice that it was shutting.

The inspection of the viaduct, according to the Highways Agency, looked at 1,000 weld joints. Of those, 64 needed repairing with plates.

The inspection team had carried out 52 by Sunday and are now working to finish the rest, including the new crack.

What is uncertain is when it'll definitely be finished. Mike Penning, the Roads Minister, said it was "highly possible" it will be finished by Thursday.

If it's not ready by then it will be a huge embarrassment as the Olympic family arrives on Monday and the M4 bus lane is meant to be reactivated by then.

However, there will probably be weight restrictions on the viaduct in the short-term.