Erm, while Central London has these things fairly widely (mainly smaller branches of chain stores, obviously, given it's Central London), even around other slightly further out affluent West London areas (Notting Hill, Shep Bush, Chiswick, Barnes, et al.) the chain stores are still being just so slow in rollout.
It's a right pain asking staff who are usually absolutely clueless – today in East Sheen highstreet Waitrose, they just looked at me like 'what are you talking about' blank faces when I asked them.
Great training the personnel depts are handing out here; it's all guesswork, when even asking customer service desks too, as they just don't know what availability/limits they even do. :|
Pity. As at this rate, we'll be waiting years for even decent London coverage, nevermind national.