I can remember the proper name for them but it's along the line of Armed Emergency Response Teams. Watching tapes and a short training exercise the amount of trigger discipline and weapons handling is amazing.
The qualfiied officers are Authorised Firearms Officers who will also stand up the equivalent of SWAT teams as needed for each constabulary.
London has Specialist Firearms Officers as well who are a standing set of SWAT type teams. Several have written some very good books about their experiences, Steve Collins especially.
The main thing in the UK is that armed officers who discharge their weapon, let alone kill someone, face extremely rigorous scrutiny by an external agency. This combined with no specific legal protections means that a police officer shooting their weapon is very rare, it happens a handful of times across the UK each year.