Thanks all, appreciate the fast responses.
Note that I explicitly ruled out widening col B.
I had been assuming that cell B2 would be treated identically to B1, as text. Both have a General format. And I also tried Text format in vain.
However, prompted by your replies, I now realise that Excel must be insisting on treating it as a date. So I'll simply prefix it with a single quote character.
Terry, UK