Tube Lines, the much-maligned private infrastructure firm responsible for running and maintaining the Northern Line, made a pre-tax profit of £63 million in the past financial year.

It has also been revealed that Terry Morgan, the Tube Lines' chief executive, enjoys an annual salary of £500,000.

Barnet's London Assembly member Brian Coleman accused Mr Morgan of doing little more than spending his time making excuses for problems on the Northern Line.

The Conservative councillor, a long-time Tube Lines critic, said: "Terry Morgan needs to stop making excuses and fulfil the obligations of the contract that his company successfully tendered for. If it wasn't capable of performing the job, it shouldn't have applied.

"The Northern Line, which I have used daily for almost three years, is fast becoming a joke, an absolute disgrace, and making commuters' lives a misery. In fact, throughout the past three years I can safely say that I have not noticed any significant improvement in its performance."

A Tube Lines spokeswoman said: "Tube Lines did not make a profit from the Northern Line, which has proved the most troublesome of the three lines for which it is responsible. Whilst Tube Lines acknowledges the need to improve performance faster on the Northern Line, year-on-year service reliability has improved by 30 per cent and the number of incidents has dropped by 16 per cent since 2003.

"The Northern Line is the most heavily loaded line on the underground in terms of passenger numbers and has some of the oldest assets, but performance is getting better. Tube Lines is committed to improving the performance of the line to the standards it has achieved on the Piccadilly and Jubilee lines."

London Underground last month threatened Tube Lines with "serious contractual remedies" if improvements were not made. The "misery line" recorded more than 5,000 delays between May 2005 and May 2006, confirming its status as the worst-performing Tube line.

  • Northern Line passengers face disruption over the bank holiday weekend with the line suspended both ways between Camden Town and East Finchley, and Finchley Central and Mill Hill East, as Tube Lines carries out engineering work. Bus replacement services will operate.