Tube Lines is still negotiating with London Underground to close sections of the Northern Line for weeks or months.
It claims that under three weekend possessions in March, it completed three year's of engineering work by operating continuously.
An LUL spokesman said that permission would only be granted if:
Tube Lines had the resources to carry out the work
that there was sufficient economic benefit
that work carried out would be at a cheaper rate than under the PPP and the cost savings would be reinvested in the Tube.
The Northern Line is the busiest Tube service, carrying over 660,000 passengers every week day.