Safety experts are checking the capital’s theatres after about ten square metres of plaster from the Grade II-listed Apollo Theatre plummeted on to the stalls below, dragging a section of the balcony with it on Thursday night. The debris struck members of the audience and filled the theatre with clouds of thick dust.
More than 700 people were inside the Apollo – which was 45 minutes into the National Theatre’s performance of The Curious Incident of the Dog in the Night-Time – when members of the audience started screaming as parts of the ceiling caved in.
Some of the injured were taken to hospital on board London buses as the emergency services dealt with the incident in Shaftesbury Avenue in the heart of the capital.
Most were discharged shortly afterwards, having been mainly treated for cuts and bruises.
Mr Johnson said the response had been “exemplary”, adding: “I would stress that, although it is too early to say what caused this collapse, and whilst this was a serious incident, London’s world-renowned theatreland is open for business and thousands of theatre-goers will rightly be out and about tonight and over the weekend.
“Westminster City Council and the Society of London Theatre have assured me that all safety checks for the West End’s historic theatres are up to date but, as a precaution, further checks have already started and will continue throughout the day.”
A Scotland Yard spokesman said they had ruled out criminal involvement and the investigation into what happened will be handled by the council.
Nicola Aiken, the council’s cabinet member for community protection, said: “Each historic theatre is unique and we have no reason to believe this is other than an isolated incident.
“We have confirmed today with the Society of London Theatre that all theatres’ safety checks are up to date.
“However, as a precaution, all historic theatres are carrying out further safety checks today.”
She said she could not “speculate” on how long the investigation would take and added that council staff would leave “no stone unturned” in investigating the cause.
One line of inquiry will be the effect of adverse weather on the 100-year-old building.
Forecasters confirmed there was an abnormally high concentration of rain, hail and lightning strikes in London between 7pm and 9pm on Thursday night, with nearly 15 per cent of the average monthly rainfall for one area in December falling in an hour.
A MeteoGroup forecaster said: “In terms of that particularly heavy rain that we had overnight, the heaviest rain was between 7pm and 8pm.
“There was 8mm in an hour in south London, and we had reports that some of that fell as hail.
“For 8mm to fall in an hour is quite a lot. The average December monthly rainfall for Heathrow, for example, is 55mm. When you put it in that sort of perspective, it was a lot.
“We also had 15 lightning strikes that occurred during the evening yesterday. They were fairly scattered around London, but I can confirm there was one in central London.
“That is a lot of lightning, especially for quite a concentrated area. When you look at the rest of the UK, there is not very much, and it’s quite unusual for them all to cluster in one location.”
A spokeswoman for Nimax Theatres, which owns the Apollo, said performances had been cancelled until Saturday 4 January.