How do I tell my parents that I don't want to do law?

Tell them that you can still be a doctor at the end of the course if you follow through with psychology. Perhaps if they care about money look up how much a psychologist in London specifically can earn and hopefully that'll appease them. It sounds like you might be worried about the effect of your image regarding the rest of your family and honestly you just have to be comfortable with your own options and if your parents support you even better, you and them are the only people that really care about your education and future life. Don't be ashamed! Their is nothing worse than going to uni and not doing a course you like, you'll become extremely fed up or you'll end up quitting or you'll struggle the whole way through dreading it the whole time. I do music and I love my course I saw my flatmates that picked courses to appeal to family members, for money or for it being an " intellectual " subject, they struggled the whole way through with extreme stress or they quit or they're re-starting on a completely different course this year. Explain to your parents that this is a very serious decision and that you know best and you know that this is the course you want to do.

Neither to say, people's mental health is constantly deteriorating in our stressful day and age, that's guaranteed work for future you.😉 (sorry I have a dark sense of humour)

HAHAHA that last sentence made me laugh! That is really good advice and I appreciate you doing something you genuinely enjoy such as music, thats very admirable. Reading what you said, its made me realise that what my other family think/expect really isn't important, especially not in the long run. Thank you for helping me acknowledge that, I feel more encouraged to tell them how I truly feel now.