Shouldn't that be a BSO now?!!!!!
No, FISO remains a FISO, just as an ATCO remains and ATCO.
Back to what Classicwings said, there's nothing wrong with starting out as a FISO, but there's a world of difference between FISO and ATCO.
If you cant get NATS training, I strongly suggest the ATSA route at a regional airport, during which time you could easily fit in the training for a FISO licence on the side at an appropriate airfield.
This would give you a very good grounding for ATCO training, by combining ATSA duties at a busy airport with the bare basics of controlling involved within the FISO world.