The four Central Trains vehicles have been withdrawn from service while the "precautionary" checks are under way.

The 10-year-old trains normally run on lines between Lichfield, Redditch, Coventry, Wolverhampton, Walsall and Birmingham.

A spokesman for the company said the cracks had not posed any threat to passenger safety.

He said they were "minor" faults, measuring up to two inches, and were on the under-frames of the Class 323 electric trains.

They were spotted during routine checks.

"As a responsible train operator we have decided to remove these trains from service until they are fixed."