Train drivers will be balloted on strike action unless rail companies respond positively within seven days to demands for a package of improved safety measures.

The union is demanding the installation nationwide of the Automatic Train Protection (ATP) system as well as in-cab radios.

It is also seeking "an urgent meeting" with Deputy Prime Minister John Prescott.

General Secretary Mick Rix said: "Failure to respond within seven days will bring the train companies into dispute with this union."

Aslef is also seeking assurances that there will be no more reductions in driver-training programmes.

Rail operators companies have said it is too early to respond to such demands.

Mick Rix: "Safety must be put before cost"

The installation of ATP was recommended by the report on the 1988 Clapham rail crash in which 35 people were killed. The fitting of the fail-safe system is estimated to cost about �1bn.

The government announced this summer that a new train protection warning system (TPWS) would have to be fitted across the network by 2004 at a cost of about �150m.

Mr Rix said TPWS would not prevent trains travelling at more than 70mph from going through danger signals.

He said: "Some people have branded TPWS as a 'mickey mouse' system. I would not say that but we really need ATP.

"We will be making it quite clear to the deputy prime minister that we have evidence that Paddington and other accidents could have been avoided."

Mr Rix added: "I think the public, rightly, is now making a clear demand that safety must be put before cost.

Lord Macdonald (right) visited the scene with John Prescott

Earlier, Transport Minister Lord Macdonald said he wanted the issue of train protection systems to be resumed as quickly as possible.

He said the train protection warning system the government was investing in would catch two-thirds of trains passing through red lights.

ATP, which is fitted to some faster trains, was not suitable to being fitted in the entire network.

A full inquiry has been promised into Tuesday's rail disaster by Prime Minister Tony Blair, who met survivors and the staff which treated them on Wednesday morning.

Transport Minister Lord Macdonald said he also wanted the issue of train protection systems to be resumed as quickly as possible.

He said the warning system the government was investing in would catch two-thirds of trains passing through red lights.

Transport Minister Lord MacDonald: "We were distressed as others were by the delay"

ATP, which is fitted to some faster trains, was not suitable to being fitted in the entire network, said Lord Macdonald.

He said: "There is a technical dimension which has to be looked at, it isn't simply a question of costs."

Lord Macdonald also said the inquiry into the 1997 Southall rail crash will be asked to consider safety questions arising from Tuesday's accident.

The accident happened miles from the scene of the Southall crash, in which seven people were killed when two trains collided two years ago.

A public inquiry into that collision opened last month after the train operator Great Western Trains was fined a record �1.5m.