Welshboy, I don't know if I hope you are correct or not. It would seem that at present 900hrs is going to be achieved before a rolling 12 months is achieved. Not working in the terminals would leave BA with the worst option - that being to stand you down with no pay.
Have BA provided a written interpretation of Sect 5 of the Mixed Fleet contract, sub headed, Job title, duties and flexibility. In particular the comment '...it is an express condition of your employment that you agree to undertake any other duties or roles that the company may reasonably assign to you from time to time on either a temporary or permanent basis. These may include a ground role at the company....'