The future of the frequencies that radio mics operate on is part of a wider discussion about the allocation of spectrum after the switch from analogue to digital TV.

Many in the entertainment industry are concerned that Ofcom has given no indication of who will control the spectrum after 2012.

Spare channels

Plans to auction the spectrum could see theatres, festival organisers and broadcasters that rely on radio mics squeezed out by those with deeper pockets, such as companies offering mobile services.

Even if radio mics can still operate, sharing the spectrum with others could lead to major interference problems experts say.

"Ofcom needs to have a serious discussion with parties involved in using radio mics and find a way of achieving a sensible outcome," said Brian Copsey, secretary of the Association of Service Providers, a body which obtains spectrum for the entertainment industry.

"We need a way forward to ring-fence this spectrum on a geographical basis. It is important to the whole UK economy. West End theatre sees 12.5m visitors each year and not one of those shows work without radio mics," he added.

Radio mics operate on the so-called interleaved spectrum - spare channels used by broadcasters - which is being reviewed in the lead up to the switch-over from analogue to digital.

Serious problem

Ofcom proposes that the spectrum be put up for auction, which experts worry will see it bought up by mobile phone companies or digital broadcasters.

"Once the auctioning process is started there will be a range of organisations that are very interested. It is prime spectrum but there are no provisions in Ofcom's proposals to put in place any system for radio mics," said Mr Copsey.

If users of radio mics are forced on to different frequencies, it would mean thousands of pounds of upgrades which theatres and other organisations could ill-afford, he said.

The other alternative - digital mics - is not a magic bullet, despite it being pushed as the way forward by regulators, said Mr Copsey. As well as the expense of buying the new mics there have been other issues in their development, not least the fact that they are less spectrum-efficient, he points out.

Increasingly organisations that rely on radio mics, such as the BBC, are realising that there is a serious problem.

"Ofcom doesn't appear to realise the importance of radio mics in modern production setups," Jules Silvester, resource manager in BBC studios, told the BBC's in-house magazine Ariel.

"We should raise this issue now before it's too late. We need to retain the digital interleaved spectrum for programme makers and special events," he said.

Ofcom maintains that its plans for spectrum are essential if it is to be used to its full potential

"In future there won't be guaranteed access to radio spectrum, which will inevitably create a certain degree of uncertainty," said an Ofcom spokesperson.

Bringing spectrum to the market is not simply about making money though, he said.

"Ofcom's objective is not to raise revenue for the Treasury but to make sure it is used to the full. Spectrum is an extremely valuable resource - like land or water," he added.