We don't really have a 'stand-out' company that everyone goes to, like Gavin de Becker or Icon or a few others over in the states (although GdeB operate over here too); we have a few 'usual suspects', a few that operate under the radar who I won't name as they like to stay unknown and exclusive, or they mostly have their own teams who travel with them, get around SIA licencing by being 'PAs' or 'drivers' while over here and sometimes hire a local old fart like me to be 'local liaison' to show them around.
If you're fishing for a name to go spam with your CV and ask for a job, forget it, that's never worked in the CP world anyway, you need to prove yourself.