We sold bunches of these in the AYH store on Spring Street in NYC. With 2 D cells they weighed a ton but were state of the art at the time (tons better than wonder lights). Attachments for the left fork blade were hard to come by but friends always cleaned out the shops of them whenever they visited the UK. I sent our listmeister photos of the ones I still have and he is posting them on the cr site somewhere.
I never knew but Berec is an acronym for:
BEREC = British Ever Ready Electrical Company
Another bit of trivia courtesy of Stephen Bauman, a long time NYC AYH bike leader: what is the meaning of "BS3648" cast into the red plastic lens of the BEREC rear light?
Len Diamond
Ridgewood, New Jersey USA