Post script: Once the main body of the campaigners had arrived to the Bank of England area, the Metropolitan police then cordoned off exits from this area, not permitting demonstrators or indeed members of the public who happened to be in the area leave the vicinity. A problematic police technique (or fad) called containment also sometimes called corralling, or aptly 'kettling' because it can produce a similar effect as a blocked boiling kettle.
At around 3.30 in the afternoon the police discreetly opened one way out for people to leave the demonstration area by a small side street, but it was not obvious, one had to discover this route by luck or chance.
The photographer Richard Wolff left at this time, so he did not directly witness the later circumstances of the tragic killing of a passer-by Mr Ian Tomlinson shortly after being assaulted by a riot policeman near the Bank of England. This incident was recorded on video by a concerned member of the public and widely and internationally distributed.
Though areas of the police lines or cordons blocking the people are perhaps likely to be more stressed, however the policing generally that was directly observed by the photographer within the centre parts of the Street Theatre - Bank of England G20 demonstrations, appeared to him to be reasonably calm, (needless to say, excluding the later above appalling incident).