Very early Freeview set-top boxes nearly all had RF modulators built into them, so that they could send a signal to a TV set's aerial socket. (Similarly, early users of VHS recorders would connect them to their TV's aerial socket, simply because one or both of their devices didn't have a Scart socket). So there might be quite a few of those old set-top boxes around. (Very few later set-top boxes had RF modulators built in, as it added to the cost and most people could use Scart connections by then. However they could still be purchased separately, to go in between a set-top box and a TV's aerial socket).
Interestingly, the fact that a Freeview set-top box handles colour signals doesn't, in itself, mean that a colour licence is required. However if someone with a B&W TV set uses any form of recording device (whether that be an old VHS recorder or the latest digital recorder) then, because it records programmes in colour (even though they won't be viewed in colour), a colour licence is required.