I would find it a little surprising if a UK university only took your A'levels into account, and entirely ignored the fact that you had done a BA and done well in it.
However your best option will be to telephone the admissions officer for some of the universities you might be interested in, and ask them whether, if you have an undergraduate BA, but you want to study a 3 year LLB as a second undergraduate degree, you would be considered on the basis of your BA results or only your A'level results.