Dualling some sections of track had been previously suggested

The line to London Waterloo is the only alternative for travellers from Devon and Cornwall who want to avoid delays on the line to Paddington.

The Paddington line is closed because of last week's Berkshire rail tragedy when seven people were killed as the train derailed after it hit a car.

The MPs said the improvements on the single track were long overdue.

Longer trains

In their campaign, the MPs are saying existing single track sections between Exeter and Salisbury should be made into dual tracks.

The government rejected this improvement, believing that longer trains would cope with capacity.

However, most trains are already six coaches long, which is the maximum that can be accommodated without extensive platform lengthening.

The MPs say the situation has become more serious with the strong possibility of a new town being built between Exeter and Broadclyst, putting pressure on the rail network.

They are calling on the government to take action before the situation "becomes impossible".

The 1735 First Great Western service from London Paddington to Plymouth on Saturday 6 November was described as a "tragic accident" by the government after a report found no fault with rail equipment or staff.