Our press has (understandably) pretty much focused on the UK's actions but this has been a coordinated embargo enacted by 12 other countries too (Ireland, Holland, Belgium, Canada, Denmark, Finland, France, Iceland, Norway, Poland, Portugal, and Sweden).
If you read or saw Mark Carney's speech at Davos in January the wheels were set in motion then. Establishing alternative trade routes & getting agreement on wording etc from a dozen countries takes time so whilst it's been recently announced, the reality is that it's been cooking in the background for most of the year.