Originally Posted by
Frostchamber
Range of factors in play, eg: it fits with the PM's view of the UK's place in the world post-Brexit; debt is cheap at present; Johnson doesn't start in a good place in terms of his relationship with Biden, and this sort of move should help; the UK has also slipped in terms of being seen by the US as the best and most reliable ally; it's a useful and timely bone to throw for unhappy Tory MPs; and it can be presented as supporting skilled jobs and the economy at a tricky time.
And probably acknowledgement that recognising the world is a much more dangerous place than we have been pretending for the last 15 years or so, means doing something about it.