UNION leaders last night demanded assurances from train operators over the level of cover in the event of a strike by firefighters.

The Rail Maritime and Transport workers union warned it could take industrial action if guarantees over safety were not forthcoming.

Particular concerns have been expressed over safety on the Tyne and Wear Metro if the armed forces are drafted in to replace regular fire crews.

Both the RMT and drivers union Aslef have already written to Nexus, the operators of the Metro, in a bid to clarify the position.

Last night, Bob Crow, general secretary of the RMT, said he was not prepared to see the lives of his members jeopardised by inferior cover.

He said Nexus had until the end of today to give assurances about the level of fire cover.

If this was not possible, a strike ballot would be called with any industrial action likely to coincide with walkouts by firefighters.

RMT regional organiser Stan Herschel said he was reluctant to see safety "put down to chance".

He said: "The professional firefighters that we have are conversant with the railway system and have the necessary specialist equipment and communications to do the job.

"If they were to take industrial action that might well leave workers in a vulnerable position and we would have great reservations about safety."

A Nexus spokesman said: "We believe that the concerns raised by the unions over a possible firefighters' strike may be premature but we recognise the need for the question to be asked.

"As a rail operator, Nexus has written to the Railway Inspectorate to clarify the situation should the fire brigade go on strike.

"The Tyne and Wear Metro have in place effective arr-angements for the safe evacuation of passengers from sub-surface stations."