The British public were tonight warned they must stay indoors or face a fine as the battle against coronavirus ramped up another level.Prime Minister Boris Johnson said all shops apart from food stores and chemists must close immediately.Meeting friends will also be banned, but one form of exercise a day will be allowed.The lockdown will be in a place for an initial period of three weeks, Mr Johnson confirmed.Announcing powers not seen since wartime, Mr Johnson declared: "From this evening I must give the British people a very simple instruction - you must stay at home."Because the critical thing we must do is stop the disease spreading between households."People will be allowed to leave their homes for the following reasons:He added: