PASSENGERS were shocked when debris rained down on to carriage windows and their train ground to a halt outside Box Tunnel.

The 8.45am London Paddington to Bristol train was travelling through the tunnel last Thursday at 10.10am when passengers heard a sudden bang.

"Debris from the lining of the tunnel hit the train causing three cracks in the outer skin of the windows," said a spokesman from Network Rail, which maintains the line.

After hearing the noise the driver brought the train to a stop and went to check the damage.

Seeing there was no serious damage the driver reported the incident and continued onwards to Bristol.

Network Rail inspectors later closed the tunnel for three hours.

The inspectors believe the debris came from the lining of the tunnel and had come loose.

The spokesman said: "It is not a common problem and the tunnel is checked on a weekly basis. The inspectors checked the tunnel and it was fine. The line was re-opened at 1.05pm."

A spokesman for First Great Western Trains said other trains had to be diverted.

She said they would not be paying compensation to the passengers of the 8.45am train.

She said because the delay caused by the stop in the tunnel was minimal it was not necessary to offer compensation.