More than one million former ITV Digital subscribers are being asked to pay a one-off �39.99 fee for their set-top boxes or return them. BBC News Online asks what right the company's liquidator has to bill the subscribers and what will happen if they do not pay?

Why have the liquidators taken this step?

When ITV Digital collapsed last May a million screens went blank overnight and creditors - including 72 Football League clubs - were left nursing heavy losses.

Consumers are being regarded as 'low hanging fruit' by the liquidator, but we have serious questions about the value placed on these boxes.

Allan Williams, Consumers' Association

The liquidators of ITV Digital, Grant Thornton, appointed to get the best possible deal for creditors, have already sold the firms' premises and furniture.

Back in September even ITV Digital's chief marketing tool - the knitted monkey - went under the auctioneer's hammer.

But one of the biggest assets, the set top boxes installed in subscribers' homes, has been left alone.

If ITV Digital is no longer operating how can the liquidators justify charging ex-subscribers?

ITV Digital may be defunct but the set top boxes can pick up the free-to-view BBC digital channels - such as BBC Four and News 24.

Some High Street stores are selling reconditioned ITV digital boxes for this purpose.

In the run up to Christmas the liquidator could be seen as cashing in on renewed public interest in digital television prompted by the BBC takeover of the platform.

Does the liquidator have law on its side?

A spokesman for Grant Thornton told BBC News Online that customers who signed a subscriber contract and had not bought the box were "legally bound" to either return it or pay for it.

ITV Digital set-top boxes may be past their best

Allan Williams, senior policy adviser for the Consumers' Association agreed that the liquidator was on strong legal ground.

But being right in law is no good without enforcement.

If ex-ITV Digital subscribers refuse en masse to either surrender their boxes or pay the fee it would be prohibitively expensive, not to mention a PR nightmare, for the liquidator to take them all to court.

In addition, according to Mr Williams those ex-subscribers who choose to pay the fee may not be getting a good deal - as in some cases the technology used in ITV Digital boxes may be past its sell-by date.

"Consumers are being regarded as 'low hanging fruit' by the liquidator, but we have serious questions about the value placed on these boxes.

These older boxes are much slower than the newer Freeview decoders, which are available for around �100, and may not be able to be upgraded in the future."

What if the liquidator gets its way and ex-subscribers either pay up or surrender their boxes?

If Grant Thornton's move gets a sizeable number of set-top box holders to pay up it will be a major coup for the creditors.

However, the �39.99 fee goes only a small way to recouping the cost of making and installing the boxes originally.

But if ex-subscribers choose to surrender their boxes, or even bin them - as collecting set top boxes from hundreds of thousands of homes may be uneconomic - it could prove a major set back for digital TV in the UK.

At a stroke, the number of homes receiving digital TV would be slashed.

As a result, the government might have to put off its plans to switch off the analogue TV signal within a decade.