The title already has the question. If I have a master's degree, can I use it to apply for another (in UK)? I have completed my master's degree (GPA 4.0/4.0) at my home country (situated in northern Europe), and I would now like to do another one-year MSc course at a top university to swap fields. The thing is, my BSc degree is clearly below average (lack of motivation during the first years... is costly), so I really hope this would be possible. I also have 4 peer-reviewed publications.
Yes, of course you can, since you are changing fields.
A friend of mind never finished his bachelor degree and had years of work experience and wanted to get into a master program (in the US). The program he wanted said they would take him if he had a bachelor degree but since he did not have one, he could not enter.
He went to the UK, got accepted into one master program based on his partial completion of his bachelor degree COMBINED with his real-world experience. Once he completed that master program, the program in the US (in a different field) did accept him.
So, yes, it is absolutely possible to do this.
I think what your real question is whether an admission committee will overlook your poor performance during your undergraduate since you have a master degree. It would help to know what your performance was during your master, and how 'top' of a school you want to get into.
The publications should help, especially if they are from reputable journals. The best course is to actually submit an application. However, you should consider what you really want to achieve. If you want to do research, perhaps going into a PhD program would be better for you. If you just want to change fields, but don't want to do a lot of research, then a new master degree might be just what you need.