I bet it won't even last two-thirds of winter!
The models are still looking good in terms of a change away from this persistent mild gunk with this weekend set to feel quite different from the last few down here at least!
Both GEFS and ECM-EPS show that after the weekend there are two options on the table. One is a return to zonality, albeit not the silly levels of warmth we've had recently. The other option is a pattern which includes some actual cold weather, which would feel absolutely perishing compared to the daily excursions into the teens we've had of late.
A winter wonderland still isn't likely, but the building blocks are still failling into place. The top of the stratosphere is still going to see an injection of warmth and lower down the forecast from ECM at least is for the zonal winds to reverse above about 70N in the mid-term - a sure sign of high pressure over the Arctic!
http://www.geo.fu-berlin.de/en/met/ag/strat/produkte/winterdiagnostics/ (click Zonal Wind charts - negative numbers mean the flow is east-to-west rather than west-to-east).
It then becomes a game of seeing just where that Arctic high ends up. The more interesting runs (in terms of cold) have it linking in some shape or form with a ridge from the Azores - it's the sort of thing we need to be looking out for in terms of seeing whether we get merely average weather or a cold spell. For now, it's too far out to draw any conclusions other than that the past few weeks worth of seemingly endless mild gunk look unlikely to be repeated after this weekend.