Britain's early plan to combat Covid-19 was a "disaster" and "awful decisions" led to the government imposing lockdowns that could have been avoided, said Prime Minister Boris Johnson's former top adviser.

Dominic Cummings, who left Johnson's staff late last year, made his comments in a series of tweets just days before he is due to give evidence to members of parliament about the government's handling of the pandemic.

"If we'd had the right preparations + competent people in charge, we would probably have avoided lockdown 1, definitely no need for lockdowns 2 and 3," Cummings wrote on Twitter.

"Given the plan was AWOL/disaster + awful decisions delayed everything, lockdown 1 became necessary."