Ceri JC

I agree that they are, in themselves, an utter waste of time. The only instance I can see where they might be useful, is when the media latch onto the content of a petition and getting it more time in the news. There's the chance it could become a 'hot topic' in the press and that might sway the government. Still, in terms of amount of time/effort spent on your part versus likelihood of effecting change, it is a very inefficient means of doing so. Writing to your MP is only marginally more effort and vastly more likely to make a difference. Make sure it's checked by someone who can write formally if you're not used to letter writing; it'll carry far more weight.

With regard to this particular petition and them doing this in Westminster, it'll happen elsewhere soon. The rest of local government follows London and the rest of London follows Westminster. What happens there, will usually spread out to other areas over the following few years.