This is about how metaphors can skew things.

I've just read a letter the UK Prime Minister sent to MPs who left the Conservative party last week. I was struck by the number of times the word "deliver" was used. Five. Delivering a strong economy, delivering world class public services and three delivers to do with Brexit.

For me delivery is a transactional word. The doing of something with a clear start and end, like the delivery of a baby, a speech or ironically a letter. It seems odd to use it in the context of something continuous and indefinite like an economy.

Driven by idle curiosity I counted the number of times the word or derivatives of it have been used by Prime Ministers in each of their annual party conference speeches over the last 40 years.

In 70s and 80s the word was used hardly at all, just a few instances in each decade. It picked up in the 90s when it was used 11 times. But the delivery of delivery really got going with Blair's premiership. In 2000 he used it 8 times (this was the year that the PMs Delivery Unit was set up) and in 2004 a solid 12 times. And interestingly, a few days later, Howard scored a thumping 19 in his leader's speech to the Conservative's conference - although to be fair 6 of those were part of rhetoric about the Delivery Unit. Overall: 38 times, by PMs, in the noughties.

This decade, delivery is really delivering - 44 so far with two years still to go. Cameron was about as prolific as Blair - they both averaged 4 per speech. May has stepped things up to an average of 7 in her three speeches. And not to be outdone Corbyn has matched her, deliver for deliver in his.

The delivering of things seems to have become a thing. Perhaps in the case of politicians it polls well. There's something comforting about the idea of clicking to buy a policy reassured that all we have to do is to wait for it to flop onto the mat.

But things don't work that way. Delivery is a poor metaphor for bringing about complex change. If we keep saying it we will fool ourselves we have more control than we really do and heighten disenchantment when things don't work out as promised.

I said skew but I think I mean screw.