The fireworks display at Blackheath is happening on Saturday the 4th of November.
Here are two links with some information on it:
The View London page is a bit weird, it says "This year marks the 401st anniversary of the Gunpowder Plot and as such, visitors to Blackheath can expect something special." So what's so special about 401 years? Are they just trying to say that they forgot it last year?
Anyway last years show was great and I hope to go again this year. It's free too :)