LONDON, Jan 18 (Reuters) - A former senior adviser to Boris Johnson who claims the British prime minister lied about a party held at his residence during a COVID-19 lockdown will be questioned by an investigation into allegations of rule-breaking, the Mirror reported. British media have reported that at least 11 gatherings took place at 10 Downing Street - the prime minister"s official residence and office - or in other government departments between May 2020 and April 2021, when COVID-19 rules limited how many people could meet socially. An internal investigation is being carried out to establish the facts. Dominic Cummings, an architect of Britain"s departure from the European Union and a former senior adviser to Johnson who left government under acrimonious terms in November 2020, will be interviewed by Sue Gray, a senior government official who is carrying out the investigation, according to the Mirror. Cummings said on Monday the prime minister knew in advance about a drinks party at his residence during the first coronavirus lockdown despite later claiming he had not realised it was a social gathering. Johnson last week apologised to parliament for attending a "bring your own booze" gathering in the garden of Downing Street on May 20, 2020, but said he had thought it was a work event. Cummings claims Johnson misled parliament because he had agreed the drinks party should go ahead. "The PM agreed it should," Cummings said in his blog. "The events of 20 May alone, never mind the string of other events, mean the PM lied to parliament about parties."