One point worth considering - BC's TP insurance is "primary specific" insurance, which means that they cover everything in a claim against you. Other types of insurance may result in the insurer demanding details of whoever else might cover you (i.e. house insurance) and insisting that they settle up their share of the bill, meaning that you've made a claim on that policy too.
I don't know what cover LCC (or others) provide, but it's always best to be aware of these things.
For my money, joining BC was a no-brainer. In addition to the £10,000,000 of TP insurance cover, I got a free set of Pod lights (RRP £45), I get 10% off at
Halfords and
Chain Reaction and
Evans*, plus legal support.
I've had the £32 I paid (it's since gone up to £35) back several times over just using the discount at Halfords - which is off everything, even sale or other reduced stuff.
* - it seems that Evans aren't officially on the discount list, but I've asked when making a purchase in store and got the discount.