A DISAGREEMENT over cost could see tube trains becoming more crowded and improvements on London Underground abandoned, the London Assembly has said.

Transport for London (TfL) and Tube Lines, the maintenance firm for London Underground, cannot agree on the cost of upgrade work.

A report by the London Assembly has found plans to reduce congestion and improve access to stations are in jeopardy as a result.

In 2008, London Underground gave an estimate of £4.1billion to complete improvements between 2010 and 2017, but Tube Lines gave the cost as nearly double that at £7.2billion.

According to the London Assembly, the gap has put pressure on TfL's budget and progress has slowed on several projects.

After maintenance firm Metronet collapsed in 2007, TfL began completing their projects, but about half the 150 refurbishment plans set to be finished by 2010 have been set back as late as 2017.

The London Assembly have called on TfL to rework plans to include the mounting cost of upgrades.

TfL and London Underground have also been asked to be more open and accountable about progress.

London Underground has resubmitted its contract terms to Tube Lines.

Tube Lines has until June to respond.

A Department for Transport spokesman said: "We have already agreed a generous long-term settlement with TfL, providing more than £40bn for London transport over the next 10 years.

"It is now for TfL to manage this to deliver the high quality transport its users expect."