By Torin Douglas BBC News media correspondent

Murphy headed BBC Three and its predecessor BBC Choice

Stuart Murphy's decision to step down as controller of BBC Three to join an independent production company raises two questions.

Firstly, what will it mean for the channel? And secondly, is there a "brain drain" from the BBC to the independent sector?

The second issue was raised by the industry paper Broadcast, which pointed to a succession of TV executives who have left the Corporation this year to go independent.

BBC One controller Lorraine Heggessey has become chief executive of Thames Talkback; director of sport Peter Salmon (also a former BBC One controller) is running the Television Corporation; controller of entertainment Jane Lush has set up her own production company, and several other top comedy and entertainment talents have joined the independents.

Two-way street

Murphy is becoming creative director of RDF Media, the maker of Wife Swap and Faking It, one of several independent producers which are spreading their financial wings.

Regulation changes mean independents can exploit more of the rights in their programmes, and this has attracted City interest - which in turn has helped them to poach top BBC talent.

Many believe such movement between the BBC and the commercial sector is healthy

But the system works both ways. Heggessey was replaced at BBC One by the former head of Thames Talkback, Peter Fincham, in a virtual job swap.

The BBC director general, Mark Thompson, was poached last year from Channel 4.

Its director of television, Jana Bennett, was previously at Discovery.

Many of the front-runners for Murphy's job at BBC Three are currently running commercial channels.

Many believe such movement between the BBC and the commercial sector is healthy.

In any case, TV channel controllers cannot stay in their job forever. It can be grinding and all-consuming - particularly in today's highly competitive TV environment - and fresh views and ideas are essential after a few years.

Government setback

Murphy has been controller of BBC Three and its predecessor BBC Choice since 1999.

He turned BBC Choice into a younger, more entertainment-focused channel - doubling its audience in nine months - before relaunching it as BBC Three, aimed at 16 to 34-year-olds.

There was a setback - the government initially rejected the BBC's plans for the channel, insisting there should be more news and other public service content.

Under Murphy, BBC Three has developed some big hits and award-winners - most notably the comedy Little Britain, which started on Radio 4.

It's won more than 70 awards, including six from Bafta and 15 from the Royal Television Society.

The BBC management contested this view, but the channel's strategy is now under scrutiny by the BBC governors

It has been a technological innovator, pioneering interactivity and previewing its new comedies on broadband ahead of their TV transmission.

But last year the channel was criticised in a review for the government by Patrick Barwise of London Business School.

He was unimpressed by its main news bulletin at 7pm, saying it "achieves nothing and attracts tiny audiences" in head-on competition with Channel 4 News.

Overall, he said, the channel's low audience and high cost made it poor value for money.

The BBC management contested this view, but the channel's strategy is now under scrutiny by the BBC governors.