WRONG!
I've worked, the whole time I have been at uni. After Christmas is peak time for students looking for jobs. This is also the worst time of year to be looking for unskilled part-time work, which is probably what you'll be looking for (catering/bar/shop work). I used to work as a banqueting supervisor at a big hotel in Nottingham. Come Jan/Feb, there used to never be any work for the waiters and bar staff that were already on the books, let alone new ones! Things used to get so slack that I'd even have my hours cut-back. After a year or so, I decided to move over to pro waitering (better money, regular hours). You'll find it hard, however, to walk into one of these jobs. Everyone wants to work for tips, and the best places are usually fully staffed most of the year. THE BEST WAY to get yourself into one of these places is to get in there during the summer. They've lost some staff through graduation, and a looking to replace them. By January, they'll have all the staff they need.
The Students' Union job shops are a help, but the work isn't normally that good, and the pay is usually wank.