Tube Lines has bought computer cards, old chips and other equipment which are now out of stock.

Company bosses said they had to use the internet because some of the signalling systems on the Tube were so old.

A spokesman said some items bought were up to 20 years old. "It highlights the need to upgrade the system," he said.

We now have the spectacle of privateers pocketing huge sums of public money searching for obsolete equipment on eBay Bob Crow, Rail Maritime and Transport union

Tube Lines, a consortium which manages the Jubilee, Northern and Piccadilly lines, said it needed to make sure it had the appropriate supplies.

"In some cases we have cloned equipment but where parts and other pieces of equipment are out of stock we will buy them," added the spokesman.

A problem with cab radios continued to cause delays for travellers on the Northern line on Wednesday, with services cut by up to 40%.

Bob Crow, general secretary of the Rail Maritime and Transport union, said the public was promised a better Tube, but in return there has been derailments, falling maintenance levels and communication breakdown.

"Targets for improvements have already been put back to somewhere over the rainbow, and we now have the spectacle of privateers pocketing huge sums of public money searching for obsolete equipment on eBay," he said.

The cab radio system is due to be replaced next year.