NTL, Britain’s biggest cable company, has instructed Goldman Sachs to sell its network of television tranmission towers to cut its £3 billon debt by about £1.2 billion.

Goldman is drawing up an information memorandum, detailing the tower arm’s financial position, which will be sent to potential bidders in the next fortnight.

NTL has been encouraged to sell off its transmission business after its rival Crown Castle UK was bought by National Grid Transco, the infrastructure group, for £1.1 billion. The field of would-be buyers is likely to be dominated by venture capitalists, such as the Carlyle Group.

National Grid Transco said that it was unlikely to make a second purchase so soon after it had digested the first.

A sale of NTL Broadcast’s transmission network could be achieved as soon as the end of the year, it is thought.

Among other potential buyers are the private equity groups Apax, Blackstone, Cinven and the Terra Firma vehicle run by Guy Hands.

NTL was forced to postpone a sale of its last attempt to sell the transmission towers in December 2001, as its impending debt restructuring depressed the price of the network — one of its largest non core assets which accounts for about 12 per cent of its revenues — below £1 billion.

The transmission operation, called NTL Broadcast, helps to beam television pictures to domestic aerials via a network of radio masts dotted around the country. It is a standalone business that has no synergy with the company’s cable network.

In the first half of the year NTL Broadcast earned £63.5 million and its income is fairly stable at or around £30 million a quarter. During the same period, NTL earned £397 million on an underlying basis.

The cable company has considered selling the mast operation before, but until now the company has been reluctant to part with the business — largely because it thought it would receive a poor price.

Nasdaq-listed NTL stumbled into Chapter 11 in 2002 after running up too much debt, and had to reach agreement with creditors to wriggle out of $10.6 billion in borrowings. Since then, the performance of the company has stabilised, although it has only just begun to generate cash.

NTL shares fell 1 per cent to $60.33 yesterday.