From September onwards our clients keep asking us when they should be doing their "last cut". I think that in London there is really no such thing, that is unless we get a really cold winter like last year and everything just stops! Grass doesn't stop growing until the soil temperature drops below 5 degrees and stays there so in our City, in a mild winter, these low soil temperatures might just never happen.
We have been mowing our regular clients every other week since November (with the added bonus of hoovering up leaves) and we will give them a monthly cut in Dec, Jan and Feb as they will probably need it. Grass just loves being pruned (it responds by getting thicker and stronger) so it is a great investment for next year. Lawns that are left to get too long over the winter months thin out and tend to trap additional moisture encouraging moss and diseases.
Our Tip is to keep mowing as long as you can see the grass is still growing: We mow at 1.5 inches all year round and you may well find us out there on a non frosty day mowing in January!