Wales' Covid "firebreak" lockdown in October 2020 was the "correct decision", according to Boris Johnson's former communications chief.
Lee Cain told the UK Covid Inquiry that the Welsh government was right to impose the "decisive" and "politically advantageous" three-week action.
During it people were told to stay at home and pubs, restaurants, hotels and non-essential shops had to shut.
Gatherings, indoors and out, with those not in your household were also banned.
Welsh First Minister Mark Drakeford called it a "short, sharp, shock to turn back the clock, slow down the virus and buy us more time".
Without action the NHS would not be able to cope, Mr Drakeford told a press conference at the time.
The Welsh lockdown, which would eventually be mirrored in England two weeks later, led to a clash with the UK Treasury.
It saw then Chancellor Rishi Sunak decline to bring forward the new Job Support Scheme (JSS) to replace the furlough in time to top up Welsh wages, leaving many employees fearing redundancy.
In a letter to Mr Drakeford he rejected implementing JSS - which would have covered 67% of wages - a month sooner because of "limitations in HMRC delivery timescales".
In his witness statement to the inquiry, Mr Cain said a meeting in the Cabinet room in Westminster on 21 September 2020 heard "overwhelming expert opinion that if the (UK) government did not take action in the form of a circuit breaker, Covid would once again spread rampantly across the UK".
"That would leave no other option than a longer more restrictive lockdown in the months ahead," he said.
The statement then went on to say that "by late October Covid rates had continued to rise and were at risk of getting out of control."
Eventually then Prime Minister Boris Johnson announced a lockdown for England, which began on November 5, 2020 and lasted for a month.
The UK-wide inquiry began in June, and could go on as long as three years, and will predominantly look at the UK government's approach to the pandemic.
The Welsh government has refused calls for a Wales-only inquiry and has backed the UK-wide exercise,