Hi,
I'm a current psychology third year so am able to tell you about the PCN course since it overlaps lots with standard psychology.
Firstly, while there are only about 50 people on the PCN course, there are 200 who do straight psychology and during 1st & 2nd year you have all your lectures with them - that means BIG lecture halls! Similarly, 1st year labs are combined with straight psychology and it's only in 2nd year that you have PCN-specific labs (2 hours per week with people doing only your specific course).
In first year, you get 2 coursework essays (about 1500 words each) per term - which aren't that bad - and also 2/3 lab reports (2000 words each), which again are fine as long as you don't leave it until the last minute.
In second year, you have 2 bigger lab reports per term and no coursework essays. Then, in third year you have your third-year-project (equivalent to a dissertation) and have a more flexible choice of modules. PCN students have to take at least 1/3 of their modules in specific topics (such as Neuroscience etc) in order to meet the cognitive neuroscience requirements.
In general, the workload is fine (must nicer than lots of other courses) as long as you aren't a crammer and do the required reading for 2nd and 3rd year as you go along rather than leaving it until the holidays.
Hope that helps and let me know if you have any more questions!