You can do a law degree in the UK, but it doesn't give you the right to practice without undertaking additional courses and training. Becoming a solicitor in the UK is a 7 year ordeal. I assume becoming a barrister is similar.
NB Given the multiple legal systems in the UK there will be a lot of variations - e.g. to become an advocate here in Scotland (our equivalent of barristers) I think you could do that in 4 years: 2 year LLB, 1 year training in a law firm and then one year devilling (where you are an Advocate's Devil!).
Edit: Might be out of date - its a while since my wife did her 2 year LLB and then qualified and became an advocate.
3 year (or more) undergrad, plus 5 years becoming a lawyer.
Or, in Scotland, typically 4 years undergrad (it can be 3y), plus 4 years.
Or the 7 years the parent comment said.
Edit: Relatively few people (I think) do a first degree and then immediately go to law school - most people I knew who did that were changing to law after some other career and had a degree in something unrelated.