Hey there, welcome to Fluther :)
Unfortunately I don’t know a whole lot about the other fields you refer to, but I do know quite a lot about the academic study of Psychology and the sorts of courses on offer in the UK (I completed my BSc in Psychology a number of years ago, did a Masters last year, and am currently working on my PhD in clinical psychology).
Psychology definitely shouldn’t be seen as a quick option, particularly if you’re interested in practising clinical psychology (working in the NHS, treating patients with mental health problems, etc.). If you’re interested in actually being a professional psychologist, you need to do an extra three years postgraduate training after you finish your undergraduate course. An undergraduate psychology degree doesn’t qualify you at all to practice professionally or see patients, etc. It isn’t a vocational degree, and the vast majority of people with undergraduate psychology degrees do not go on to work as psychologists.
From what you’ve written, it sounds like you’re thinking about being a clinical psychologist (it’s what most people think of when they think of professional psychologists!). To get onto the DClinPsy (the 3 year graduate training programme for those wishing to be clinical psychologists), it is notoriously competitive. People typically have (at the very least) several years work experience in assistant psychologist positions in the NHS, or jobs that involve a lot of patient contact. Many of the people applying also have Masters degrees or PhDs (I’m currently doing a PhD (research degree) in psychology, and a lot of my fellow PhD colleagues are planning to apply to the DClinPsy once they get their PhDs… just to let you know the kind of standard you’d be up against!). You can see there that the training alone is, at the bare minimum, 6 years (3 year undergraduate course, 3 year DClin). As many people have extra postgraduate qualifications when they apply, that potentially takes you beyond 6 years (although postgraduate qualifications aren’t mandatory for admission to the programme). There would also be several years work experience involved in between your undergraduate degree and your DClinPsy – it’s pretty much unheard of for people to get in straight after they graduate from their undergraduate degree, and most applicants typically apply for several years before successfully gaining a place.
I absolutely don’t want to discourage you if this is your goal, but there’s such a huge amount of misinformation about what a psychology degree is and what is qualifies you to do, that it would be really bad for you to make a decision based on something that wasn’t really true. I’m really happy to talk to you about this in more detail if you’re interested :)
In the mean time, I’d strongly recommend that you have a look at the British Psychological Society website as they have a great deal of information on careers in psychology, and the sorts of training options available. I also recommend the Psychology forum at The Student Room website, as there are many good threads there about getting qualified as a professional clinical psychologist.