One of the units mentioned can't afford to 'manufacture it's own ATCO's' (...although home grown staff do, in my experience, make good ATCO's who are already settled in the area and familiar with local procedures.) The cost of all three ratings, taking into account the course costs, salary, cover during training etc. is in excess of £65K.
Subsequently, the afore(not)mentioned unit would ideally look to recruit fully rated, experienced ATCO's wherever possible. That said, it doesn't pay huge salaries and is bl00dy busy!!...these are hardly the right incentives to attract new recruits, but the hours are good and the cost of living is still relatively sensible.
The likelihood is that it will have to employ partially qualified ATCO's and fund the extra training required to fill future vacancies, a policy that has benefitted more than one poster to this thread already!!
One of the units mentioned is hoping to increase it's complement of ATCO's in the relatively near future and will have a requirement to fill 2 more vacancies due to retirements in the medium term, so if Booklady, or anyone else with more than 1 rating, preferably all 3, a Met. ticket, OJTI rating and a sense of humour would care to send me their CV, at least I'll have somewhere to start when I get the nod from the Board