Should I study an undergraduate or postgraduate course?

If you only have your school qualifications or a qualification below degree level, then you should be looking at undergraduate courses. These are the standard degree level courses in the UK and usually take 3 years.

You should only be looking at a postgraduate course if you have an undergraduate degree (or the equivalent). If you want to do a postgraduate course, you should start with a Masters (which is usually only 1 year) and then go on to do a PhD.