Your link shows the Dartford Crossing, an M25 bridge miles downstream of the City. The Blackwall Tunnel runs under the Thames at Greenwich and afaik just has the old school hanging metal blocks at height https://maps.app.goo.gl/N5xSF148ggLVTDtS8
It doesn't surprise me too much that police are on standby, a closure of either tunnel or bridge has a major effect on traffic all over London
It doesn't surprise me too much that police are on standby, a closure of either tunnel or bridge has a major effect on traffic all over London