Michael Portillo has announced his plans to step down as MP at the next election.
The former Defence Secretary said: "In a number of ways I have lost my enthusiasm for the cut and thrust of the chamber and my contribution has diminished."
He has been in Parliament since 1984 but is now keen to "explore opportunities in the media, public bodies and the arts."
The announcement came after Conservative leader Michael Howard had offered him a job, which he felt he could not turn down without explaining his decision to leave parliament.
What is your reaction to Portillo's impending departure from politics? Send us your thoughts.
This debate is now closed. Read your comments below.
I have always admired Michael Portillo as a politician but his increasing role as a commentator and his other interests make me wonder how he can represent his constituency.
When we vote for MPs, do we vote for part-time ones or full-time ones? Too many MPs today seem to spend a lot of time doing things that have scant relationship to their elected roles and more to do with self-promotion. Whatever happened to public service?
I didn't always agree with him whilst he was under the sway of the last Tory government, but over the last few years Michael Portillo has been one of the few politicians who has felt able to express his views in a forthright manner. Not only do I salute him for this, but also wish that he could lead his party in the same manner. I hope for his return.
Now the Tories need to get rid of Howard as soon as possible and then they just MIGHT, at some time in the future, become electable.
Mike Sterland, England
You need character in a politician and Portillo has it by the bucket load. Never flustered and always sure of his beliefs, he has been one of the great Conservatives of modern times, respected across the House. I want him to go away and explore new adventures and come back and do what he does best, fight for the Conservatives and serve his country where he is needed most.
Terry Dunning, East Timor and England
I am not surprised. As a Tory he was never, in my view, the ideal candidate for leader. Cabinet yes. Tony Blair will not be jumping for joy at his departure; he has too many problems in his own camp to sort out first. Let's be clear, Tony Blair has a real job to do to prove he is the best person to lead this country, so far he has failed miserably.
John McGowan, UK
Portillo does come across as refreshing and engaging, and at one time I would have rejoiced to see him as Tory leader but the current climate - huge majority, huge problems - needs something more than just a Clear Blue Blair. It needs somebody to well and truly burst Blair's bubble.
Mike Page, UK
I think Portillo has seen what the Tories need to get elected and has taken personal measures to enhance that chance. Michael Howard's position has undermined any thought of that happening. Portillo has now done a quick swerve so he is not going to be part of the laughing stock the Tories are going to become under Howard.
Richard Davie, Scotland
It's a shame in a way. Since his famous electoral defeat he became human and is now the most likeable politician in the country. Although we'll still be able to see him on the telly, it would be nice to see him be a leader some day (soon).
Portillo was a great politician. I was desperately sorry he never became party leader. But something tells me the Tories will modernise without him, become the natural party of government again, and in a couple of years we'll all have largely forgotten this ultra-talented nearly man. No disrespect to the excellent Portillo - but the Tories have suddenly found their way and they are on the road back to power, with or without Portillo.
Robert, England, UK
Tony Blair must be jumping for joy. With Portillo's departure, so goes any chance of the Tories gathering the youth, liberal, humane, and anything left of right-wing vote. RIP unelectable Tory party next election.
Joe Thomas, UK
Shame, but I thought this was going to happen. He was the one chance for a potentially successful Conservative leader. Like they say though, you've got to be mad to want to be PM anyway.
Portillo is the most natural and persuasive political speaker I've ever heard. This combined with his libertarian views would make him a far better PM than Blair, Brown, Howard or anyone else you could name.
This is very sad news. I would have voted for Portillo, had he become Leader of the Conservatives. But I'm not entirely surprised. He never was as coldly ambitious as the media made out, and I wish him the best of luck for the future.
Steven Forrester, UK
Thank you and best wishes for the future, Michael. This is a huge blow to the Conservatives, their most obvious candidate to be Prime Minister has decided to turn away. A problem to those trying to modernise the party, and to all in the country who wanted to see the Conservatives have their top man as leader. Sorry Mr Howard, Portillo was in a different league.
Nick, Wales, UK
I am rather sad to hear it really. I have watched Michael Portillo on many political shows especially this week. He came across a very sensible intelligent person, with a relaxed honest attitude that was very refreshing. Coming from a stand point of liberal inclusiveness with a more right wing economic agenda he could of beat Tony Blair if the Conservatives gave him a chance. Shame they are too narrow minded to do it.
Dominic Smith, UK
Portillo knew that he could never be compatible with Howard - they are light-years apart in their politics. What choice did he have?
Michael Portillo is the Tories lost leader. His election as leader would have sent the clearest signal to the country that the Conservative Party had changed. However, those brave Tory MPs at Westminster decided to go back to the future by democratically electing the Prince of Darkness. What a wasted opportunity!
Portillo could and should have done far more with his talent. As such, he probably chose the wrong party as an expression of his political and personal views. The Tories certainly don't have the social conscience or socially cohesive thinking that Portillo clearly backs. I hope he uses his time outside Parliament wisely, and in particular that he stands up for the rights of minority groups (except Tories!)
Andy Millward, UK
I'm deeply sorry to learn of Michael Portillo's decision to step down from politics. He represented the acceptable face of the Conservative Party and would have been in a good position to lead after the next election. The Party has been hi-jacked by a right wing clique who used clinical skills to dispose of Iain Duncan Smith. Howard will never attract the many former Conservative voters and activists like myself who do not recognise the current party.
Portillo was our last hope of modernising the Conservative Party which has an average membership age of 67 years. I hope he regains his enthusiasm for politics and returns in the future. Politics is the poorer without him but least he can give his honest opinions from the sidelines.
Paul Leslie, Scotland