Dominic Cummings, a former top aide to British Prime Minister Boris Johnson and architect of Brexit, is expected to take aim at the government during a marathon grilling from lawmakers on Wednesday.

Cummings, who resigned as Johnson's chief advisor in December, has unleashed a barrage of explosive attacks against his former boss's coronavirus policies and financial transactions in recent weeks.

He has accused the UK leader of lacking competence and honesty, as well as his administration, of having "appalling ethics." He is a controversial figure who carved out a remarkably influential position during Johnson's first 18 months in office.