My understanding is that it's been around since at least September and at least a few countries.
My feelings? That the government are using it to justify the u-turn from "It would be inhuman to stop people seeing their families at Christmas" to whatever their line is now.
3 weeks to flatten the curve.... (which we did) ..... to this and what is going to come next.
The reality is that it's probably a good thing, a virus mutating into a less harmful/more easily transferred strain is exactly what you would expect it to do. The new strain may not be any more deadly than a common cold coronavirus... there's no evidence to say otherwise yet, so why the panic?