having dug around a few websites (not helped by FAA's one appearing to be offline at the moment) I find that Serco bought Barton ATC who are operating as part of the FAA Contract Tower Initiative. Towers in this programme are all "Level 1 VFR Facilities"
In the UK these would probably be staffed with FISO's - hardly comparable to Heathrow/Gatwick/Manchester + the rest.