AIUI, NYE in London is covered by a joint SJA/LAS operation. SJA provides most of the ambulances for the event itself, along with ambulance crews, first aid posts, first aiders, doctors and nurses and the pack-horse part of the FIT teams. LAS provides techs and paramedics for the FIT teams, and ECPs for some of the first aid units. The idea with the FIT teams is that between 3 people they carry most of the contents of an ambulance to the patient on foot and assess and treat on scene, because there's generally no quick way to get an ambulance through the large crowd to the patient. The same joint SJA/LAS FIT teams are used at other large events, notably Notting Hill carnival where I they first started.