A �2m communications system for part of the London Underground (LU) may have to be written off.

The new radio system has been under development for seven years, but has proved unreliable and has never been used.

LU managers have said the technology is now so out of date it will have to be abandoned.

A more advanced digital system is due to be introduced across the network in 2004.

This was the best deal in terms of radio systems that were available to us at the time. Rob Mason London Underground

The Ultra High Frequency (UHF) radio was part of a �300m contract in 1995 to supply new trains on the Northern Line.

It was supposed to replace the old Very High Frequency (VHF) system in 1999 and revolutionise communications with drivers.

But because it proved undependable its implementation was delayed until 2004, which is when LU plans to switch to a digital system.

LU's Rob Mason told BBC London: "This was the best deal in terms of radio systems that were available to us at the time. Things have moved on a lot in 10 years."

Steve Grant, from the Tube drivers union Aslef, said: "We've had to put up with some right rubbish over the years and there has been some serious incidents - breakdowns in equipment and failure.

"The system needs this, and the sooner the better. I want to know why this system is not in place."

Scrapping the system will cost the company about �2m but it says it will be able to salvage some of the equipment.