It was a fire on some scaffolding. Seemed a huge reaction for a fire, so must have been more to it.
Luckily I could see my bike from outside the cordon. I asked a Cycle Sheriff politely if I could retrieve my ticket home. He wouldn't let me in, but he took my keys and fetched my bike for me. So happy to report a nice police action.
"Police responsible for tail wind" shocker!