More than 20,000 migrants have arrived in the UK so far this year after crossing the Channel.
Some 300 people made the journey in five boats on Tuesday, according to Government figures, suggesting an average of around 60 people per boat.
This takes the provisional total for 2023 to date to 20,101, the Home Office data shows.
This is around 20% down on this time last year when more than 25,000 people had already made the journey, according to PA news agency analysis of the figures.
There have been 5,369 people detected crossing the Channel so far this month, compared with 8,631 recorded in the whole of August 2022.
Pictures of some of Tuesday’s arrivals showed a dinghy packed with men and boys, some without lifejackets, perched on the sides while their legs dangled in the water.
Labour’s shadow home secretary Yvette Cooper said the Prime Minister had “failed to get a grip” on Channel crossings.
But Mr Sunak continued to defend his “stop the boats” plan as he faced questions from broadcasters and insisted the Government was making progress.
He urged people to “have confidence” in his plan as he claimed the lower number of Channel crossings compared to last year showed it was “working”.
Mr Sunak previously played down suggestions that the lower number of crossings compared with last year was linked to poor weather conditions rather than policy decisions.
But this summer has seen more unsettled weather compared with last year when there was a spike in crossings in August.
While June 2023 was the warmest on record, July and August have been much more unsettled, with a sequence of low pressure bringing wind and rain.
Summer 2022 was the fourth warmest on record for the UK and the warmest on record for England, with heatwaves in each of the three months.
Sacha Deshmukh, chief executive of Amnesty International UK, said: “This is another reminder that the Government’s failing migration policies won’t stop people making perilous journeys to seek asylum.”
Ms Cooper told PA: “Rishi Sunak made this his top priority. He told us that his plan was working.
“And yet these figures show that he’s completely failed to get a grip.
“The Tories’ boats chaos is continuing, that’s undermining our border security and putting lives at risk.
“In the space of just a few years, the Conservatives have let criminal gangs take hold along the Channel.
“What we need is a proper plan to go after those criminal gangs and to stop the dangerous crossings that are putting lives at risk. That is what Labour would do.”
A Home Office spokesman said: “The unacceptable number of people risking their lives by making these dangerous crossings is placing an unprecedented strain on our asylum system.
“Our priority is to stop the boats, and our Small Boats Operational Command is working alongside our French partners and other agencies to disrupt the people smugglers.
“The Government is going even further through our Illegal Migration Act which will mean that people arriving in the UK illegally are detained and promptly removed to their country of origin or a safe third country.”
Mr Sunak also failed to say when migrants would be moved back onto the Bibby Stockholm barge in Portland, Dorset.
The first asylum seekers arrived on the barge earlier this month but were moved off again just days later after tests revealed Legionella – the bacteria which can cause the potentially fatal Legionnaires’ disease – was present.
Home Secretary Suella Braverman has insisted the giant vessel is safe amid threats of legal action from firefighters.
