This week the Tories were on the back foot over impending cuts in working tax credits. It demonstrated the effectiveness of Jeremy Corbyn's approach to PMQs. His use of a question from a real person demonstrating the impact of the cuts produced a response that hoisted the Prime Minister on his own petard.
The leader of the opposition planted a ticking bomb which put the government on the back foot through the week. The Labour leader repeated his PMQs tactic of asking questions submitted by the public, saying he had received 2,000 emails about tax credits. One was from a single mother who he said would be £1,800 worse off under the government's changes to tax credits.
Sure enough, the bomb exploded with an emotional intervention from a member of the BBC Question Time audience again illustrating the real impact, in this case on someone who had voted Conservative and feels betrayed.
Cameron had promised in the general election that there would be no changes to working tax credits.
Ironically Mr Cameron made his pledge on BBC Question Time election special in April. He was asked by Jenny in the audience whether it was true the Tories had plans to cut working tax credits.
He then gave an unequivocal reply.
"No, I don't want to do that. This report that's out today is something I rejected at the time as Prime Minister and I reject it again today."
The host David Dimbleby then pushed him on the detail, saying some people were clearly worried.
The PM replied: "Child tax credit we increased by £450."
"And it's not going to fall?" asked the presenter.
The PM confirmed: "It's not going to fall."
This was no slip. It was the Tory leader giving an unqualified response.
Now the government have been forced once again to give a response.
A spokesperson for Mr Cameron has said: “It’s worth remembering with tax credits ... they have increased over the years and so the spend on tax credits has gone up and up and up. If we’re going to tackle the overall welfare budget and try to move away from being a high welfare country to a low welfare country, then this is something we have to look at.”
They justify the cuts on the grounds that the bill for tax credits is too high. This is disengenuous. No doubt the bill is high, but that was as true in April before the election as it is now. There is only one conclusion we can draw. Mr Cameron knew he was giving a false answer in April. He lied.
It is also disingenuous in another way. Unemployment has fallen in large part by a massive increase in part time jobs and in those in work like the lady on question time. She set up her own small business - a nail parlour. She relies on tax credits. The government has forced many into low payed jobs and on tenuous contracts, or no contracts at all.
There are now more than 5 million people in low payed jobs. A recent report showed that workers in Britain were more likely to be low paid than workers in comparable economies like Germany and Australia.
So what is the truth on tax credits. One in five of the lowest paid workers will be worse off. That is the bottom line. Hard working families will be pushed into poverty. That is the incontrovertible truth. It means that a hard working mum on £14,500 a year with a disabled child will lose £1,800 per year in support. That is the bottom line. So who are these people?
Those who will suffer will not be simply some statistic on a spreadsheet. They will be real people such as nursery nurses. They will be real people such as carers. They will be many of the 5 million hard working people in low paid jobs. That is the reality, and it is as disgraceful as it is unnecessary.