More than 50 people believed to have attended lockdown parties at British Prime Minister Boris Johnson’s Downing Street will be contacted by police to explain their involvement, officers said on Wednesday, as they considered widening their investigation.

A statement from London’s Metropolitan Police said officers would start contacting people from the end of this week, asking them to complete a document with formal legal status on the events that have left Johnson facing the gravest crisis of his premiership.

Police are investigating 12 gatherings held at Johnson’s office and residence after an internal inquiry found his staff had enjoyed alcohol-fuelled