Fellow Brit here who literally just changed jobs and industries altogether. Disclamer, I do have a degree, but I'm about to start in a job completely unrelated to it. Couple of suggestions for you:

There are some really good resources in the UK for people who aren't sure what they want to do. I randomly went along to a job fair and chatted to lots of prospective employers. Gave me some good ideas. I also got to have a free CV session with the National Careers Service, and they offer more detailed sessions to discuss potential career options and help you with applications etc.

When I was deciding what I wanted to do instead I started by thinking about the bits I liked about my job, and what things were missing that would make me happy. Having identified a couple of things, I started speaking to people I knew who enjoyed their work about their jobs to find out more about what they do and how they got there. This actually helped me choose my new direction.

If you're not sure about uni, look into other professional qualifications that can help land you a decent job.

Finally, I noticed you commented saying you weren't sure about changing jobs with a mortgage. Whilst its not a good idea to change jobs in the process of buying a place (I was actually advised against it by the broker), once I had the mortgage it was actually cheaper than my rent so I felt freer to change jobs. Depends on where you live in the UK though.

Anyway, good luck.