Presumably Ryanair can be added to that list (if you term it "airlines with their main place of operations in the UK"). The last 2 737-800s they had delivered are reported as parked up at Prestwick at present (one for around a fortnight), and another 2 are en route from Boeing as I type. Presumably they will all need crew - and not forgetting the other 100 or so due over the next few years.