[clort]

Well, I guess nations do that all the time. Certainly I've heard of it in the last year or so.

  https://www.independent.co.uk/news/world/middle-east/turkey-erdogan-president-us-ambassador-visa-latest-a7993116.html
  http://www.telegraph.co.uk/news/worldnews/the-pope/11527987/Pope-Francis-refuses-gay-French-ambassador.html
  https://www.radionz.co.nz/news/national/254049/israel-won%27t-recognise-nz-ambassador

In a legal manner (and not because I'm a UK citizen) I presume the host nation can decline and then the proposing nation can find another one or send them anyway but risk that he falls foul of the law and the host country does not recognise any diplomatic immunity. In this case though, if the UK declines then he is still stuck in there with no way out.

I think its kind of strange really that we have spent all this money pursuing this guy for what was a minor warrant (that they wanted to speak to him) which has since been cancelled and think that we (the UK) should just say enough already and turn a blind eye to him leaving on a jet plane. Oh yeah, but the strange part is that it really seems as if its important to somebody that that doesn't happen.

[blibble]

the warrant was revoked, but prior to that he skipped bail, which is contempt of court

at worst it's a year in prison