The one I always come back to is the National Road Pricing Proposal a few years ago - a big petition (nearly 2 million) completely killed it. It does require a lot of people to get noticed though.

https://en.wikipedia.org/wiki/Road_pricing_in_the_United_Kin...

Then we keep kicking off serial petitions, until the ignoring of these petitions becomes a story and makes the news - and hopefully wakes everyone up.

[edit: How many signatures does it take before the debate has to be followed by an action?]