Transport secretary Alistair Darling will this week agree an extra £8 billion of funding for the rail network.

The cash is needed to cover the rising costs of maintenance and overruns on major projects.

The funding is expected to be made up of £5 billion in direct grants and £3 billion in loan facilities.

The announcement will come as part of a government attempt to secure the financial future of the network as Railtrack is replaced by the not-for-profit Network Rail.

Final agreement on the deal that would see Network Rail purchase the network assets of Railtrack could come as early as today, with shares in Railtrack Group being traded on the Stock Exchange for the first time since the company was placed in administration last October.