Should I wait until the number plate change to buy a used car?

I want to change my Jaguar XF before mid-March this year because it will be coming up for it's third MoT and I know it will require some minor work, plus it's due a major service. It's about time I changed...

Is late December and early January the best time to buy a car from a dealer?

I'm think of buying a car and having narrowed it down to a couple of choices. Is December around Christmas and early New Year a better time from a buyers perspective to buy a new/used car from a dealer?