Nicky Jacobs punched the air after a jury cleared him of the murder of Pc Keith Blakelock.
He subsequently sat down and sobbed before being taken from the dock.
The 45-year-old's supporters in the public gallery including Winston Silcott - whose conviction for the murder of Pc Blakelock was quashed in 1991 - shouted "Yeah, yeah" and called out "Brother, brother" as the verdict was announced.
Courtenay Griffiths QC, for the defence, said: "I'm delighted, I think the jury reached exactly the right verdicts. Now I have to go and see my client."
More top news
The London Mayor insisted he was "not saying that nationalists are somehow racist or bigoted" after outraging SNP supporters.
The teenagers, aged 19 to 15, appeared in custody at Westminster Magistrates' Court on Saturday, supported by their families.
Parker Dairies moves home after 120 years on Wood Street in Walthamstow