It's relatively easy to combine "part time" professional flying with an ATCO career in NATS.
Our shift patterns and annual leave are "set in stone" and we can therefore give reliable availability to a prospective flying company in chunks of 2 or 3 (or more) days. These companies can use us to provide rostered days off for their full time pilots as well as normal "known in advance" trips.
The issue of secondary employment is of course a valid one, but all NATS pilots that I know have had no problem with authorisation. There is no connection between flight duty periods and SCRATCOH (this has been established officially with SRG) but it is generally agreed that no flying/ATCO duties will be seperated by less than 10 hours.
It should go without saying that these days, a pilot who is well versed in ATC procedures/slot times/phraseology etc is a positive asset to any flying company.
It should also go without saying that an ATCO who is well versed and current in modern IFR aircraft operations can be a great asset to his unit and NATS in general..........I know I am !!!!!???? JOKE GUYS!!