It is this simple. The Crown Prosecution Service is now looking at the cases of 30, yes 30, Tory MPs and agents, who have been investigated for breaking spending rules at the last General Election.

The allegations have been probed by 14 police forces after claims that the Conservatives’ ‘battlebus’ campaign broke legal spending limits in several key marginal seats.

The Tories have already been in deep trouble over their new election techniques, where busloads of outsiders flood into winnable seats to round up crucial extra votes. This was a way of making up for the Tory party’s severe loss of active members, who used to do this donkey work. But it is sailing very close to the legal wind.

Last month they were hit by the Electoral Commission with a record £70,000 fine – the maximum – for failing to declare their spending. The forces involved are Avon & Somerset, Cumbria, Derbyshire, Devon & Cornwall, Gloucestershire, Greater Manchester, Lincolnshire, Northamptonshire, Nottinghamshire, Staffordshire, West Mercia, West Midlands, West Yorkshire and the Met.

These cases are likely to result in some charges (I have no idea how many) in the next few weeks, probably just before polling day. Trials, assuming these go ahead, will be much later in the year and might not reach verdicts until well into 2018.

If there had been no election, any convictions could have meant MPs found guilty being forced to stand down, and elections being rerun. A General Election makes this much less of a threat, especially if Mrs May manages to increase her meagre majority.

This menace has been worrying the Cabinet for some months, as it has become clear it will not go away. And it is a far better explanation of the Prime Minister’s change of heart than her rather weird and incoherent speech in Downing Street. I happen to think she is a naturally truthful person and meant what she said when she previously declared several times that she was going to stay on till 2020.

But the expenses allegations, which started as a cloud on the horizon no bigger than a man’s hand, have grown and grown. I suspect her advisers have been telling her she cannot risk them coming into the open late in a Parliament when, perhaps, the economy is not doing well, or EU negotiations are going badly or Labour has a new leader.

As a result of this semi-secret crisis, the Tory campaign this time will have to be a good deal more cautious about such things, which may weaken it, especially if the campaign goes wrong – and this is not impossible.

Even now the affair could be highly damaging – but early in a new Parliament, with a secure majority, the Government should be able to weather it far better than if Mrs May had soldiered on. But all elections are risks. It is amazing how often governments lose control of them.

The highest number of registrations was on the day itself, with 147,000 people registering online after Theresa May fired the election starting gun, along with 3,364 paper forms being submitted.

This was the biggest total recorded for a single day since the EU referendum campaign in 2016.