The government's plan to introduce private companies to maintain the London Underground has been approved by railway inspectors.

The Health and Safety Executive (HSE) says the arrangements "will provide an effective safety management system for the Tube".

However, the backing of the plans by the HSE has been criticised by the main union representing tube workers.

On Wednesday the Rail Maritime and Transport Union (RMT) announced a 24-hour strike over the issue.

It is a disgrace that the HSE has ignored our warning

Bob Crow

The strike will take place from 2000 BST on Wednesday 17 July to 2000 BST on Thursday 18 July.

The government's Public Private Partnership plan (PPP) for London Underground has proved highly controversial.

Workers are concerned that commercial pressures and new management structures could affect the safe running of the Tube.

London Mayor Ken Livingstone and his transport commissioner Bob Kiley are also opposed to the PPP and have launched a High Court challenge against the plan.

'HSE has failed'

Transport Secretary Alistair Darling said: "I am pleased that the Health and Safety Executive has accepted London Underground's revised safety case.

"The government has always said that the PPP will not proceed unless it is safe, and today's decision brings us a step closer to delivering �16bn of investment over the first 15 years of the 30-year deal - money the Underground desperately needs."

RMT general secretary Bob Crow said: "It is a disgrace that the HSE has ignored our warning not to approve London Underground's safety case prematurely.

"We believe that the HSE has failed in its duty to ensure that our safety representatives are consulted fully and that we are given access to documents that have so far been withheld from us.

"The HSE has failed miserably after a string of national railway disasters, and now it has failed our Tube members whose safety they are supposed to safeguard."