Here is a range of possible outcomes from today confidence ballot in Theresa May.

There are 317 potential voters: Charlie Elphicke and Andrew Griffiths have the whip returned for the day (if not longer).

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Emphatic May win

For May: 250

Against May: 67

A quarter of those eligible to vote comes in at 79 MPs.  At below a quarter, a win on this scale for the Prime Minister would be decisive.

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Clear May win

For May: 225

Against May: 92

A third of those eligible is 106. With opposition below this level, May’s win would be marked though perhaps not overwhelming.

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Problematic May win

For May: 200

Against May: 117

Once the opposition to May climbs above a third of the electorate, it becomes harder to assert legitimacy.

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Marginal May win

For May: 175

Against May: 142

This total of votes against the Prime Minister isn’t far off half – 159.  She would surely find it hard to hang in this circumstance.

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May defeat

For May: 150

Against May: 167

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So where is the danger zone for May – the range at which senior Cabinet Ministers and/or the 1922 Committee move against her, and tell her to go, as some of Margaret Thatcher’s ministers did in 1990?

Where it should be is very much a matter of individual taste, prejudice and judgement.  We would have thought that opposition of about a third of Tory MPs would indicate a very substantial loss of confidence.

But as we pointed out this morning, John Major was able to hang on in the 1995 leadership contest with over a third of Conservative MPs against him, having won the College Green post-vote spin war decisively.

Where it is may be different. Our rough finger to the wind test is that the danger zone is somewhere between 110 – 125 votes against May and somewhere between about 210 – 225 votes for her.  The 215 mark seems a reasonable enough test of strengh.

Readers will have worked out that these figures presume no abstentions or spoilt ballot papers, which won’t happen real life, and which complicate such calculations.