Section 27 legislation allows police to move someone from a specified area for a period of up to 48 hours. No offence needs to have been committed for the act to be enforced: the legislation gives police the power to move on people who they say pose a risk of alcohol-related disorder.
This is meant to be a specified locality but in the instances we’ve heard of police have moved people across the entire country under threat of arrest if they don’t comply. No hard evidence appears to be required, and no crime needs to have been committed.
The legislation was clearly designed to allow the moving on of small numbers of individuals who have been misbehaving under the influence of alcohol - for example, clearing areas outside of nightclubs at closing time. It was not designed to enable, in effect, football banning order to be imposed by the police on an entire pub.