Assuming you took one and got an A*, A*ABB isn't that much better, given that the A* was achieved 10 years later. I think at this stage you should ascertain which firms have a hard limit and which look at things holistically - for the latter your degree performance, application and work experience should outweigh your BTEC results if good enough. There are also plenty of strong firms who either have no strict A Level requirements or require ABB:
Mishcon de Reya,
Pinsent Masons,
Freshfields,
Clifford Chance, etc. etc.
Of course if you simply want to do another A level then of course do so, I just doubt it would massively increase your chances even at those firms with the hard limits - chances are if they have the hard limit in the first place then they'd prefer the grades to be achieved at the same time.
Of course, I don't even have a TC yet so feel free to wait for Jessica's opinion.