NATS airports ATSAS start on 20k + 4.4k shift allowance.....going up to 27k + shift.
Maybe you should try to get a NATS assistant job wherever you can....there are many internal ATSA vacancies that come up within NATS which you can then apply for. These posts only get externally advertised if they can't be filled internally.......which is rare.
Of course as suggested, you could just apply to CATC. But being an assistant for a while can give a great insight to the job of a controller.