Update: A3 forms are now available here: Forms for electrical contractors - IET Electrical , but these are not electronically fillable - an electronically fillable version is apparently "under development", but that's what they said about the A1 forms right up to end!
I have created a Word format EIC, schedule of inspections and schedule of tests which I (will) attach for anyone who might find them useful (if someone can tell me how to attach a file here), I haven't had them proofread and know they are not absolutely identical to the ones in the BYB, so please satisfy yourself about their suitability before use. Also, I wasn't able to use Word's form controls as these don't work with tables, which I had to use to get them to look right, so you may have to use a square-root for a tick/check mark, and do some re-aligning after filling-in each form. You will also have to add in the Guidance for Recipients.