Citation needed for that. All I’ve been able to discover is this, from a UK police community site:
“ US Air Force Office of Special Investigations have several offices in the UK (which is to be expected given the USAF installations in the UK)
Naval Criminal Investigative Service (NCIS for all the lovers of the TV show) have an office in London, which falls under the control of the Field Office for Europe and Africa - based in Naples, Italy.
New York Police Department (NYPD) - the NYPD have detectives based in London as part of it’s International Liason Program.
I imagine the only ones which would have any powers in the UK would be OSI or NCIS but even then I’m not sure how that works, as OSI could have them on the RAF bases where the USAF operate but I’m unsure where NCIS Agents would utilise their powers/roles given there are no US Navy installations in the UK (that i’m aware of) so i’m unsure of what they actually do here.”
Also, some European forces have officers here:
“The French have folks around the channel tunnel and at one of the train stations in London (forget which). I think they might even be armed in some cases?
They are armed once you get through passport control, but aren’t supposed to take their weapons ‘English side’ (one would hope they wouldn’t need a sidearm once someones passed the secure area), although one French officer accidentally forgot to leave their sidearm secure when they went to WH Smiths a few years ago.
I am not sure about ‘routinely’, but I seem to recall that there was an EU-wide protocol that was signed that allowed foreign police to enter another country for reasons of expedience, such as for survellience, so long as they notified the host country as soon as was practicably possible and in any case within 4 hours.
The protocol dealt with practical issues, like carrying firearms and off weaps on foreign soil.”
