Only just discovered this thread.
Luton is not a LARS unit, so any ATSOCA they give you is 'workload permitting' bearing in mind the radar controllers aren't actually at Luton but are at West Drayton in the same room as AlanM and TDM, plus they have to do Essex Radar as well (but not necessarily at the same time).
IO540 regular radar services outside controlled airspace are available from several units such as Brize, Farnborough and Cardiff.
I agree there's a big hole in LARS availability in the south east of England; given a bit of wiring and ingenuity this hole could be filled easily (the radar displays are there as are radar heads), but the money isn't available from ATS providers who are required to show some return for any outlay, so a source of funding needs to be found. Maybe pressure on the D of T to provide funding on a 'safety' stance woild be appropriate?