I have close connection through upbringing to many small high street firms and barristers sets in one of the smaller provinces (Norfolk). From my experience, ABB will almost certainly rule you out. Though DLA Piper set their minimum requirements at ABB, without AAA+ you'll be at an immediate disadvantage to the other Law graduates from Russel Group universities. Think of Oxford University. Their minimum requirement is AAA, but if you're realistically only going to get that you probably won't get the offer.
But, 'Law' has a reputation for being rigorous, academic subject and less elite employers are more likely to gain a perception of you based on that, than the name of your university or your A levels.
After all the waffle I would say that if you are interested in reading law, then do it. It will (I believe) put you in marginally better stead that other degrees held by people with the same A levels. However, realise that with ABB your prospects of having a career in Law (via the traditional route) are severely limited.
You may want to consider the ILEX route. It will never put you on the same par as a solicitor, but it is close. Also, you could work as a paralegal for a number of years after you have your degree, and try to impress your employers into giving you a contract.