Max Wright muttered:

Most normal spinach is sown from spring onwards. It's notorious for
running to seed and needs fairly fertile soil. Much less demanding are
perpetual spinach and chard, both of which are really beets. These are
best sown in spring or summer and should produce plenty of leaves
throughout summer and autumn - they will survive most winters and start
producing again in early spring before eventually going to seed around
late April or May.

I've just sown some spinach, spinach hates to dry out and benefits from cool
conditions (doesn't bolt). The soil, however, is still warm, so it's in with
a chance, but the light may be a problem. Last winter where we are (EA) we
only had about 3 nights of frost and the grass seemed to keep growing, and
as Nick says, it's only wasting a £ if they fail.