Barry Smith wrote
Now that we have had 2-3 days of frost in the S.East of England I want
to ask if there is a chance my dahlia tubers will survive if I do not
lift them for overwintering..

We're in London and we never lift ours and never have any problems.

We haven't dug up our Dahlias in the winter for years and most are out on
our allotment which is an exposed site. The only one we have lost in the
winter was last winter and was a species dahlia and I don't think it was
frost that got it.
If you want to leave them in I always suggest planting them deeper than the
books say and don't forget to slug pellet in the spring before the first
signs of growth or you will swear the frost got them as the slugs will eat
them off as quickly as they grow.
A mulch of straw or similar will also help to keep the frost off (but it's
also liked by slugs).

--
Regards
Bob
In Runnymede, 17 miles West of London