Dont bother mate. You have to study the same modules for your B1/B2 so go straight for that.
Good luck.
Indeed that is very true, if you are a A licence holder and you wish to extend your Licence to include B1 or B2 you are required to sit the full Modules in all Categories relevant to the licence category sought, the only exemptions you will be given is you will be required to undertake a Module 7 & 10 Variant examination.
Further info on Extensions of Licences can be found in the ELGD in Section G.
ELGD | Personnel Licensing | Safety Regulation