A man with a knife has been arrested near Buckingham Palace, as Britain remains on critical terror alert amid fears Manchester suicide bomber Salman Abedi did not act alone.

The man was detained by police on The Mall just moments before the Queen passed by in a car on her way to an engagement with the Duke of Edinburgh at St Paul's Cathedral.

A picture showed the man surrounded by officers and handcuffed as he sat on the ground, while a police officer nearby held what was believed to be a large blade that had been seized.