Just checked with someone who knows - was in charge of Tannoy at the time - and the answer is that no, they're not. In fact the Sixes used quite big magnets, in a time before speaker designers were concerned about shielding, and of course the fact they're dual concentric also means there are two magnets, not just one.
That said, you won't have any problems if the TV you're going to use them next to is an LCD or plasma, as these aren't effected by such problems, but if it's a CRT I'd err on the side of caution.