Ridiculous hypothetical extremes

[h2005__uk__]

I've often wondered what it'd take for a sudden ridiculous temperature such as 30C in January in the UK or, conversely, -10C in July. I say "sudden" because I don't mean it'd be part of a hot/cold spell.

Of course we've had it on a smaller scale with the >20C temps last Feb, but what circumstances would be needed for this to go a lot higher?

I'm assuming (barring extreme climate change) that some sort of sudden sun-related event would be required? I suppose extreme cold in the summer would be achieved by something blocking out the sun on a wide scale...