By Nick Higham BBC media correspondent

So, farewell then, David Liddiment - the risk-taking director of programmes at ITV who discovered that in commercial television risk-taking has deleterious consequences for one's career.

As the professional obituaries have made clear, David Liddiment's greatest triumph was to spot the potential of Who Wants to be a Millionaire? and strip the show across five nights a week.

That was a risk, but the resulting audiences of up to 19 million played havoc with BBC One's ratings and helped ITV get close to (though rarely actually to reach) the hopelessly ambitious audience share targets set by Liddiment and the network's chief executive at the time, Richard Eyre.

Liddiment: Acknowledged commercial channels' struggles

Conversely his greatest failures were to gamble that scheduling the Premiership highlights in the early evening, rather than their traditional late-night slot, would attract a new audience and shedloads of extra advertising revenue to ITV's Saturday peaktime.

He also gambled that ITV's regional news programmes, traditionally among the network's most popular programmes, would deliver a big audience to a new teatime news at 6.30pm.

In his speech to the Edinburgh Television Festival last year, Liddiment acknowledged the problems facing commercial channel controllers who wished to innovate.

He blamed the BBC for itself being too "commercial" and leaving its rivals too little room for manoeuvre - although the experience of other countries suggests that a plethora of commercial channels is just as much to blame for the stultifying sameness of much popular television.

Liddiment spotted the merits of Millionaire

The problems are worse if you are, like ITV, the market leader.

Channel 5's director of programmes, Kevin Lygo, has been able to gamble on old-fashioned arts programming (which he hopes will appeal to an upmarket audience which has hitherto not bothered with the channel) precisely because his network comes from a very long way behind and has much less to lose if the experiment fails.

For ITV pure risk-taking is tough.

Many of Liddiment's highest-profile successes and failures were in fact with programmes which took established formulae and tweaked them.

Popstars and Pop Idol (both successes) were old-fashioned talent shows, reinvented for a new century; Survivor (a failure) was a voyeuristic reality show, but set on a desert island; Footballers' Wives (a critical success but a ratings failure) was a deliberately schlocky drama.

Successor

Luck also plays a big part, and Liddiment was often unlucky, for instance in the politicking over News at Ten and its replacement, in having to compete in the past two or three years with a BBC awash with cash, and in having to work for two main shareholders (Carlton and Granada) who took their eye off the ball big time, ploughing far too much time and money into the ill-fated ITV Digital at the ITV Network's expense.

ITV's problem now is that there is no obvious successor.

Dawn Airey (chief executive at Channel 5), Kevin Lygo, Lorraine Heggessey (controller of BBC One), Liddiment's chief scheduler David Bergg, Simon Shaps at Granada and Steve Hewlett at Carlton have all been mentioned.

All have some, though not necessarily all, of the right credentials (which include experience in both scheduling and commissioning and an ability to rub along with powerful shareholders who don't always see eye-to-eye).

Poisoned chalice

But why would Airey want to give up lucrative share options for a salaried position at a network whose future ownership and structure is uncertain?

Why would Heggessey want to quit a network currently riding high for one with a smaller budget which is struggling in the ratings? And would Carlton accept an appointee from Granada, or vice-versa?

David Liddiment has said he'll stay until the end of the year if need be. It may well take that long to find someone willing to accept the poisoned chalice from him.

A version of this column appears in the BBC magazine Ariel