David Cameron is planning to embark on the most far-reaching reconstruction of his government next week as he promotes a new generation of women and younger men in an attempt to present a youthful and modern face of the Tory party to Britain at next year's general election.

A series of older men known as the "old lags" will be sacked – or will take matters into their own hands by announcing long-planned retirements – when the prime minister carries out his final planned cabinet reshuffle before the election.

The most senior Tory cabinet ministers – George Osborne, William Hague and Theresa May – are expected to remain in place as Cameron becomes the first prime minister since Tony Blair in 1997-2001 to keep the holders of the great offices of state in place for an entire parliament.

But a much wider than expected cabinet reshuffle will see significant changes amid signs that the former chancellor Kenneth Clarke, 74, the chief whip, Sir George Young, 73 on Wednesday, and the leader of the Commons, Andrew Lansley, 57, will leave the government.

Lansley still believes that he is in the running to be nominated as Britain's European commissioner, although there are strong voices saying it would be a grave mistake to appoint the man so closely associated with the government's unpopular reorganisation of the NHS.

Theresa May, the home secretary, is expected to keep her post. Photograph: Ben Stansall/AFP/Getty

The former chancellor Lord Lawson of Blaby, a climate change sceptic, has been leading a fightback to protect the environment secretary, Owen Paterson.

The new entrants are expected to include Esther McVey, the work and pensions minister and former television presenter, and the public policy expert Liz Truss. Nicky Morgan, who attends cabinet as minister for women, may be promoted to a full cabinet post. Greg Hands, the deputy chief whip and a key Osborne ally, is being associated with a promotion to chief whip as the chancellor extends his control over the government.

Sources close to Iain Duncan Smith dismissed as nonsense claims that he would be moving from his post as work and pensions secretary. Senior figures at Westminster have been speculating that Duncan Smith, a former Scots Guards officer, might swap jobs with the defence secretary, Philip Hammond.

Osborne, who is concerned about the implementation of Duncan Smith's universal credit reform, tried to move him sideways to the Ministry of Justice in the last cabinet reshuffle in 2012. Cameron told the recent Tory summer ball that Duncan Smith was one of the three stars of his cabinet, alongside the chancellor and the home secretary.

Employment minister Esther McVey is tipped for a cabinet role. Photograph: Leon Neal/AFP/Getty Images

Friends of the prime minister are urging him to embark on a bold reshuffle because they believe he has a free hand to act as he chooses on the grounds that the departing ministers will be able to say that they served four years in government – the average length of a parliament in recent years. It is understood a large number of ministers have notified No 10 they would like to stand down from the government.

One ally said: "The prime minister can do pretty much as he likes. He has got carte blanche because he will be able to tell departing ministers that they have had a good run. There is a lot of support for the prime minister to be really bold by genuinely bringing forward large numbers of women – not simply to tweaking the odd post. Politics is all about freshness. This is a great chance to show the new and modern Tory party."

One senior Tory said: "You've got old lags preparing themselves for life after office and then the excitement and trauma of the new people. The assumption is that if it is merely a little bit of tinkering around the edges what's all this about? The hard-nosed logic is that this is the time to do quite a big change, making the assumption you are not touching Osborne, Hague and May.

"At the end of this reshuffle you want people to think this is a reinvigorated Conservative part of the coalition that are going to forcefully present Conservative party policies to the electorate. It is about momentum because you are arguing that these people could form a government on their own. The prime minister can say to a number of the people you have had a good run for your money and I have got to make space."

Kenneth Clarke could be on the way out in the reshuffle. Photograph: Peter Macdiarmid/Getty Images

Nick Clegg, acutely conscious that the five Liberal Democrat cabinet ministers are all men, is expected to promote the business minister Jo Swinson to the cabinet. But she is expected to succeed Alistair Carmichael as Scotland secretary after September's independence referendum in September if, as expected, the pro-Union side prevails. Carmichael would be praised for his role in the victory as Swinson took charge on introducing greater devolution to the Scottish parliament.

The prime minister is expected to announce the name of Britain's new European commissioner at the same time as the reshuffle. Cameron will ask Jean-Claude Juncker, the incoming European commission president, for an economics portfolio when they hold talks on the fringes of a European summit on Wednesday. Allies of the PM are urging him to consider heavyweight candidates such as former Tory MP and ITV chairman Archie Norman or the former Tory leader Lord Howard of Lympne. David Willetts, who may be replaced as universities minister by Truss, is also seen as a possible candidate.