Well somebody needs to try it out, and I am in three syndicates, only one of whom has a tame examiner to hand. In my experience, about 2/3 of biennials seem to be done towards the end of the year anyhow.
Here's the form if anybody wants a direct link.
http://www.caa.co.uk/docs/33/SRG1133Issue12.pdf . The form itself is a bit of a headache, and hasn't been fully updated for the purpose as the explanatory notes don't actually tell you which bits of the form you have to fill out for the specific purpose (it does for various other purposes), so I just filled everything out that seemed faintly applicable - I'm sure that the number of my expired Transport Canada will be useful to CAA, despite it being in the last two forms I sent them as well.
I shall report back on whether it all works out, and what it says in the explanatory card that apparently I'll get sent at the same time.
G