David Miliband is considering a role in television, in a surprise move that appears to dash his brother Ed's hopes that he can be persuaded to join the shadow cabinet.

The Labour leadership candidate, who lost out to his brother by the narrowest of margins last September, after a bitterly fought contest in which he started as clear favourite, has approached the BBC with a number of programme ideas.

It is unclear whether Miliband wants to front one-off documentaries or a series of shows, but it is thought all his proposals would involve him taking a starring role on screen.

Such a move would inevitably invite comparisons with Michael Portillo, the former Tory cabinet minister who has developed a thriving television career after his own ambitions to lead his party came to nothing. Portillo made a documentary series for Channel 4 after the humiliating loss of his parliamentary seat at the 1997 general election.

The one-time darling of the Tory right later returned to parliament but, after failing to win the leadership of his party in 2001, when he was defeated by Iain Duncan Smith, he reinvented himself as a successful presenter, pundit and documentary-maker – most recently revealing his fondness for railway travel.

There has been intense speculation about the elder Miliband's intentions since his dramatic defeat by his brother. Sources close to the former foreign secretary insisted that he had no intention of giving up his South Shields seat and said the TV idea was "one of many things David is thinking about".

They added that the plans "may or may not materialise" and strongly played down suggestions that he was thinking of following in Portillo's footsteps.

In a statement, a spokesman for Miliband said: "David is talking to a range of organisations about his interest in foreign and environmental policy."

Senior figures in the Labour party are urging David to join the shadow cabinet in order to strengthen his brother's team, following his decision last autumn to step back from a frontline role. But so far he has resisted such overtures. In an interview with the Observer before Christmas, he suggested he had not ruled out standing again for the leadership.

Asked about his transition to life on the backbenches he said: "It's not relief I feel, but it is a release … My main thought now is that there is a world out there. Sometimes, in politics, you can forget that, and get into a tunnel. There's no point in denying that it [losing] is pretty gutting. But I've got to move on."

He recently stamped firmly on suggestions that he might be tempted by an offer from the coalition government to become ambassador to Washington when Sir Nigel Sheinwald retires. Miliband has said he wouldn't accept.

A BBC spokesman confirmed: "David Miliband has approached the BBC with some programme ideas. The BBC receives suggestions from a wide variety of sources and these will be considered in the same way as any others."

The BBC added: "No substantive discussions have taken place with Mr Miliband." Industry sources believe he has held informal talks with executives at the corporation, however.

Miliband has no experience in the television industry, apart from being interviewed extensively while in government. His performances on screen are generally believed to have improved during his time in office, although he struggled to shed a reputation for being slightly awkward in front of the cameras.

His brother's supporters famously mocked him during the fractious leadership campaign by wearing badges displaying the logo: "Ed speaks human".

• This article was amended on 17 January 2011. We drew comparisons with Michael Portillo, the former Conservative cabinet minister who developed a career in TV after "failing to win the leadership of his party in 2001 when he was defeated by William Hague". He actually lost to Iain Duncan Smith. William Hague had won the leadership in 1997 and resigned in 2001. This has been corrected.