The prime minister visited three local pubs and retraced his Cornish roots at the same time as he publicly argued Britain was too risky a destination for Australian travellers.
He also visited an old jail and laid flowers for an ancestor born there in 1755.
The personal trip south of the G7 summit was not disclosed to the media and has sparked anger among Australians stuck overseas, who have described it as insensitive and tone deaf.
Mr Morrison defended tracing his family roots and insisted Australians would not see the trip as a double standard.
"It was pretty innocent ... that's massively overstating it," he told 2GB radio on Monday.
The prime minister said his plane landed north of London rather than Cornwall due to fog and the delegation stopped for breaks along the way.
"We had some lunch and stopped off in another location on the way," Mr Morrison said.
"And after the G7 on the way to the airport, we stopped at another place, which just happens to be where my fifth great grandfather was from."
Mr Morrison is not the first prime minister to go in search of family history on an official overseas trip, with John Howard previously exploring wartime battle areas around France.
But this trip was taken in the middle of a pandemic when international borders were closed and as Mr Morrison warned UK travel was too dangerous for Australians.
His stance has prevented people travelling between Australia and the UK to see friends and family.
The prime minister said he "certainly hoped" Australians would be able to travel overseas by next Christmas.
Mr Morrison said what happened overseas during the European summer would determine if and when Australia reopened its borders.
"We'll learn a lot from that," he said.
"If it's not causing serious illnesses and rising hospitalisations, then that will be important information for our medical experts to look at and give us good advice about what that means for travel."
Last year's federal budget predicted Australia's international border would reopen in mid-2022 but the troubled vaccine rollout could push back the date.