Thanks for all the input folks. My question was purely hypothetical and I hadn't expected such detailed responses. Interesting reading.
Who was the ATC provider at Luton prior to the Approach function being transferred to Swanwick ? I believe it was in-house until relatively recently.
I'm sure Southend would get to hang on to their new radar and whatever other landing aids they have, in the unlikely event of NATS coming along. The Approach/Radar controllers would still need them, they would just be seated in front of a console somewhere else.