I would be so ridiculously happy if that were the case, but I don't believe it is (unless you're aware of any recent developments I may have missed).
Unless there has been a more recent ruling, as of 1st July last year, in order to exceed 12 knots you need the following:
AIS
Flashing Light
VHF
Seats for everyone
Lifejackets for everyone
Advanced Powerboat
Thames Local Knowledge Endorsement
Lets not forget my personal favourite.....
If you are on your own its perfectly safe to not have a lookout, however if there are two of you, the lookout must be at least PB2 (with the skipper holding Advanced) otherwise its dangerous!
Also, I should point out the boat would need to be pre-approved by the PLA (i.e. you can't just turn up and assume its okay) as you have to apply for a certificate.
Off the top of my head I can't remember if you have to submit a passage plan too, they were intending to enforce that, not sure if they did bring that in or not.
http://www.pla.co.uk/pdfs/maritime/1...s_Byelaws1.pdf
Of course I would absolutely love to be proved wrong on this, as then I can bring my RIB back to the Thames!