The battle over the Tube has been delayed by yet another procedural twist.

Just hours before London mayor Ken Livingstone was due to announce on Monday his intention to go back to the High Court, Tube bosses promised to hand over key details about the PPP deals and in so doing extended the consultation period.

Livingstone, who claims that around 18 out of 135 documents are missing, is engaged with a stand-off with Tube bosses which appears set to end in the courts.

Livingstone had threatened to go legal after London Underground failed to meet his Friday deadline to hand over key details - including the crucial equity rate of return - agreed in the deals.

The mayor believes there are two possible reasons for the missing details - either London Underground and ministers are withholding information deliberately or they are still negotiating with the bidders, which would negate the value for money assessments made by Ernst and Young for Stephen Byers.

Livingstone and his transport commissioner Bob Kiley were told by London Underground they will give a full response to their request by 10am on Wednesday morning.

"They continue to fail to answer the key question which we have been putting to them since February 22," Livingstone said in a statement. "Are the PPP contracts still under negotiation?"

"The significance of this question is that, if the contracts are still being negotiated, and, in particular, if the provisions on risk transfer which are key to any judgement of value for money had not been finalised, then London Regional Transport Board had no business recommending that the government proceed with the PPP contracts."

Livingstone has told the GLA that "no reasonable person" would sign off the deals as they currently stand. He claimed that the entire modernisation programme had been removed and the contracts amounted up to little more than maintenance deals.