Their core business is enforcing the judgments of the federal courts of the US 9including arrest warrants, which is where the seeking fugitives business comes in). Along with that, they protect court officers and court buildings. They have a couple of sidelines, like running the federal witness protection programme.
They turn up in cowboy movies because, before western territories were incorporated as states, the US Marshals were the principal law enforcement agency in those territories.
As I understand it, US Marshals enforce court orders. That’s what I’d be interested in (meaning the UK counterpart.)
Scotland still has Sheriffs and Sherrif Courts. The Sherrifs are just judges these days though.
And once a year the Queen pricks their names 
We now have the National Crime Agency
No they are not, many others have the powers of arrest and detention within their duties of employment, and use these powers very regularly.
Community Support Officers.
Border Agency (immigration officials) which can be at border points or during busts.
Military Police - some of these can be shore patrols rather than full time MP - although an MP will have to authorise the arrest.
Court Officials
Prison Officers - arrests happen regularly of prisoners for indictable offences, of corrupt staff, and of visitors attempting a number of offences including smuggling and assisting an escape.
Some other prison workers may also detain prisoners for various reasons until the arrival of a prison officer.
This is a surprisingly large number of people, there are some other oddities such as some sorts of bailiffs and gamekeepers - depending upon who they are employed by.
I thought MI5 (aka the Security Service) was the equivalent to the FBI.
Rob
Not really - MI5 isn’t a police force/LEA as such, it’s an intelligence agency.
MI5 is more like the NSA - it’s nothing like the FBI.
They do some of the stuff that the FBI does, their primary role being counterintelligence
GCHQ is the equivalent of the NSA.
I thought PCSOs don’t have any greater power of arrest than any ordinary citizen?
I think the last few posts demonstrate that there’s hardly anything comparable between the two countries!
The UK Marshals would be the equivalent if I did not just make them up.
The nearest equivalent would probably be the NCA, but they’re more like a body to tackle crime that it makes more sense to tackle on a national rather than regional level.
That is correct. MI5, also, can’t arrest people. Both have to get the real police to do that. PCSOs can detain suspects who refuse to provide a name and address for up to half an hour, though.
That is, to arrest people.
In AUS, the distinction between police officers and other people is that, under the various police acts, sworn officers can arrest people on the suspicion of criminal activity, or to prevent criminal activity.
Any person here may arrest any other person who has committed a crime, and who is about to commit more crimes, or won’t give a name and address, but if I arrest a person who has not committed a crime, it’s false imprisonment (kidnapping).
Even if I think the person has committed a crime, if it’s not proved afterwards, I might be charged. Which is a powerful disensitive.
Do PCSO’s have the power to detain (arrest) people if they think it’s a good idea, subject only to administrative punishment?
Originally, a “marshal” was a servant whose job it was to look after the horses. (The first syllable in “marshal” is etymologically connected with “mare”). In a large household this was a position of some importance; especially in the king’s household, which in the late middle ages spent a lot of time travelling from place to place, and so depended on having good arrangements for horses and transport. In England, the Earl Marshal, or Marshal of England, became a high officer of state, and had wide responsiblity for the king’s household. (The office still exists, and has functions in connection with royal ceremonial.)
Various courts had their own marshals. They got that title, apparently, because the courts were the king’s courts, and they were considered to be deputies of the Marshal of England. They were charged with the court’s “household arrangements”, which included not only providing and maintaining a courthouse but also running a prison, and being responsible for the custody of prisoners.
The English courts were rationalised and consolidated in the course of the nineteenth century, and the function of running prisons was separated, and in the course of these reforms the office of court marshal disappeared.
However it was still very much around in the late 18th century, when the Americans were adapting English institutions to the requirements of the newly-independent colonies. And, as the English had no police force at the time, the marshal’s job of keeping prisoners in custody also extended to finding and arresting them, and to enforcing other court orders. The US adopted this. Since there was nothing like a US federal police force until the establishment of the FBI, US marshals did not fade away in the way the English marshals did. Even without the the running of prisons to worry about, the US marshal service had plenty of useful work to be doing.
Agreed that they’re closer, but I was looking for a US equivalent to MI5, not a UK equivalent to the NSA. Either way, I think the point is clear enough.