I called the CAA about it and got to talk to a NATS person in the end.
Are you applying as an individual or a company.
Apparently an individual can't have a call sign.
Any advances would be interesting.
I joined a flying club just to get one. Saves a lot of embarrassment when you call the tower and start off xxx Tower, Golf Alpha, sorry correction ....Golf foxtrot.
Perhaps it is just me who gets confused.