John Rentoul: Who will come top of the Cabinet class?

It is time for Cabinet ministers to get their GCSE marks, for their Government Certificate for Shuffle Eligibility. Our political editor reports today that Ed Llewellyn, the Prime Minister's chief of staff, and Kate Fall, Llewellyn's deputy, have set up a whiteboard with yellow sticky notes to plan ministerial changes.

There is a lot of information to go on that whiteboard, because this reshuffle is unusual, coming after such a long period of stability. The only changes of the past two years and four months have been David Laws, Liam Fox and Chris Huhne, each of them a fairly simple substitution, with Danny Alexander, Justine Greening and Ed Davey coming in. That means that, in most cases, there is a lot of coursework to mark.

Who, then, have been the best performers? Some candidates can be ruled out of the higher grades fairly easily. Andrew Lansley, the Health Secretary, so mishandled his NHS reforms that he had to be rescued by one of the most complicated damage limitation exercises ever mounted in British politics. What is remarkable about Lansley is that it was assumed that he would lose his job once the "pause" had achieved its purpose in getting the health Bill through the House of Lords. Now it is generally assumed that Lansley will stay in post.

George Osborne is in a special category, of axe-mad chancellors. They can sometimes earn grudging respect, but he threw that away with a tax cut for the rich in this year's Budget, since when little has gone right for him.

Admirable though he is, it is hard to think of anything Kenneth Clarke has achieved at Justice, apart from denying the space to a right-wing Conservative; while Iain Duncan Smith has said some of the right things, but his grand simplification of welfare, the Universal Credit, may yet turn out to be as politically astute as Lansley's great unifying plan to turn the NHS into a self-sustaining "clockwork universe".

With three exceptions, the rest have also yet to make much of a mark. William Hague has consistently been the most popular Cabinet minister with the voting public. It is hard to imagine, however, that this reflects a judgement on British foreign policy since 2010 – a minimal engagement in Libya still messily unresolved; a policy of watch-and-wring on Syria; and a speech last week about getting over post-colonial guilt. We like him because he was a brave British loser as Tory leader, with a sense of humour.

I think the best departmental minister of the coalition has been Michael Gove. I regard his acceleration of New Labour's schools reforms as one of the most hopeful things about this government, but many people do not take to his high Scottish whimsy and earnest moral seriousness.

If we leave him to one side – appealing for a re-mark, perhaps – there is only one Cabinet minister who emerges with credit from this assessment. The unlikely winner is Theresa May, the Home Secretary.

Last year, after she sacked Brodie Clark as head of the UK Border Agency for – she claimed – an unauthorised policy of waving people through airports if the queues were too long, opinion polls suggested she should lose her own job. This year, after G4S admitted that they could not provide the security staff they had promised for the Olympics, a poll for this newspaper found a 17-point majority supported her resignation. Yet that flurry came and went too, and the absence of queues at Heathrow was one of the great non-stories of the Olympics.

Earlier this year, she seemed not to know what day it was when Abu Qatada, the troublesome Jordanian preacher, found he had time after all to appeal to Strasbourg against his deportation. He is still in the country, but May toughed that one out too.

She is not wildly popular with the public, although 45 per cent of YouGov's respondents correctly identify her photograph (4 per cent thought she was Harriet Harman and 2 per cent Jacqui Smith) and her stock goes up and down. This time last year she was second only to Hague in Cabinet opinion ratings, although an Ashcroft poll in May this year had her at the bottom of the list with Osborne. But she is still standing, and still in one of the hardest jobs in government – even if it has been made more manageable by John Reid's splitting it from Justice in 2007.

She is responsible for one of David Cameron's more opportunistic and unrealisable promises, to cut net immigration to the "tens of thousands", an impossible job that she has delegated to Damian Green.

Through all the storms and controversies that buffet her dysfunctional department, Theresa May sails on. In the House of Commons, her technique is to repeat what she has said already and ignore any difficult questions. It is not intellectually satisfying or fun to watch, but it has been remarkably effective.

Since she was Cameron's surprise choice as Home Secretary (from being shadow Work and Pensions Secretary in opposition), she is the Cabinet minister who has emerged from the first half of this government as the most successful.

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