Many of the large employers recruit between September and December for jobs starting the following year, see link below for the National Graduate Scheme bulletin leaflet for just some of the current schemes recruiting now.
Many of the major employers often use online aptitude tests as an initial selection method. You may only get one chance to take these so will need to prepare thoroughly.
Careers and Employability offer tests in numerical, verbal and abstract reasoning to help you improve your timing and performance. See www.worc.ac.uk/careers/psychometrics or come along to discuss your application with a Careers Adviser.