Back of an envelope: Trident and jobs

As Labour has decided the prospect of spending vast sums on Trident renewal wasn't worth debating, I thought I'd do a quick back-of-the-envelope thing on the numbers being bandied about. Obviously Trident is, in terms of defence, a non-starter, as reasonably well outlined by Diane Abbott in her recent Guardian column. But people do like to go on about how many jobs it provides, so I thought I'd take a look at that.