Do any degree > apply for training contract to firms with clinical negligence practice area if want to be solicitor > do 1 year law conversion course (GDL) > do 1 year legal practice course (LPC) > do two year training contract, with hopefully a seat in clinical negligence > hope you can qualify into clinical negligence.
If you do a law degree, then you skip the GDL step and you apply for the training contract at the end of your penultimate year of study.
If you want to be a barrister in clinical negligence:
Do any degree > do 1 year law conversion course (GDL) > apply to chambers with clinical negligence practice for pupillage (1 year) > do 1 year bar professional training course (BPTC) > do pupillage (1 year training) > get tenancy and practice.
Same as above re: if you do law degree, skip GDL.
that's it in a nutshell - getting a training contract or pupillage is the hard bit and you may not get them in your first year of application. you don't need a biomed / med related undergrad degree to practise clin neg - it may be seen as helpful, but plenty of practitioners go through a law degree. many LLB programmes offer optional modules in medical law & ethics, and if you really wanted, there are also LLM (masters) programmes in medical law & ethics.
if i have made any errors, i hope someone will come along and correct me!