Should I buy a used car now or wait for January?

I’m looking for a 2 to 4 year old small SUV, budget around £15k maximum, from a main dealer. Is November a good month to get a deal, or should I wait until January, when the cars are a year older?

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...