For your information, Airports, Railway Stations, Bus Stations and land owned by the Crown Estates or various Civil Service Ministries is not designated public land.
The lawful right to take photos in the UK is not limited to 'public land'. What is public land anyway? Almost every square inch apart from a few areas of ancient common land are owned by somebody. I hope you are not involved in law enforcement. This sort of misunderstanding is why the government and police have had to issue guidelines to clarify the issue. I would suggest a public place is a place to which the public have access.
The Metropolitan Police Service’s approach towards photography in public places is a subject of regular debate.
We encourage officers and the public to be vigilant against terrorism but recognise the importance not only of protecting the public from terrorism but also promoting the freedom of the public and the media to take and publish photographs.
Guidance around the issue has been made clear to officers and PCSOs through briefings and internal communications. The following advice is available to all officers and provides a summary of the Metropolitan Police Service’s guidance around photography in public places.
Freedom to photograph/film
Members of the public and the media do not need a permit to film or photograph in public places and police have no power to stop them filming or photographing incidents or police personnel