In 2006-07, the not-for-dividend company made a post-tax profit of £1 billion compared with a loss of £253 million in 2005-06.

But the 2006-07 profit figure had to be offset against the NR debt figure, which was as high as £18.4 billion.

The figures come at a time when NR is under pressure from the Government, rail regulators and the travelling public to cut down on weekend engineering work and to improve its overall performance.

On Thursday, the Office of Rail Regulation (ORR) outlined plans for NR to make improvements for the period 2009-14, albeit with more than £3 billion less than the company had asked for.

The ORR intends to set targets for reducing the impact of engineering work, but it warned that passengers must expect to put up with weekend work for some years to come.

It was a series of engineering work overruns that caused chaos for the travelling public at the new year. The worst of these was at Rugby, in the West Midlands, on the West Coast Main Line.

Closures of parts of this line are taking place at most weekends this year as NR strives to complete a major modernisation of the line by December.

The ORR fined NR a record £14 million for the new year overruns and has told the company it expects engineering work to have as little impact on passengers as possible.

Bonuses paid to NR bosses have been the subject of controversy in recent years. The ORR has no direct say on the payments to NR bosses, which are linked to the company reaching certain performance levels.