It depends on the university - you may get offers before Christmas, or the universities may wait until after the January 15th deadline to contact you. For students who have applied before January 15th, the UCAS deadline for the universities to submit their offers to students is March 31st (unless the course is very popular, in which case it could be early May). For applications received after January 15th, the deadline is July.
My brother (UK citizen) applied in November last year and got all his university offers except one by the end of February (the last one wanted him for an interview mid-March, but he got the offer confirmation a couple of days later). When I applied back in 2000, I got my application in by the October 15th deadline (I applied for Oxbridge)... had interviews with all the universities in November and early December and I had all of my university course offers before Christmas (I got offered a place everywhere except Oxford).