Some 28,526 people arrived in the UK after crossing the English Channel in small boats last year, according to official figures released for the first time.

The Home Office published the first ever statistics measuring irregular migration on Thursday, which confirmed the Government’s official recorded annual totals.

The data reveals the total for 2021 is slightly higher than previously anticipated.

According to the report, last year’s figure compares with 8,466 people crossing in 2020, 1,843 in 2019 and 299 in 2018.

It comes as separate immigration figures showed the number of asylum claims made in the UK has climbed to its highest in nearly two decades, while the backlog of cases waiting to be determined continues to soar.

The Government’s Nationality and Borders Bill, which will make it a criminal offence to knowingly arrive in the UK illegally and introduce life sentences for those who facilitate illegal entry into the country, is currently going through Parliament.

It is not possible to know the exact size of the irregular population in the UK, nor the total number of people who enter the UK irregularly

But Marley Morris, from think tank the Institute for Public Policy Research, said the crisis in Ukraine “sheds light on the shortcomings” of the Bill, adding: “The Bill diminishes the UK’s duty to provide those who seek asylum a fair hearing and will lead to further delays to an already struggling system.”

Steve Valdez-Symonds, from Amnesty International UK, said: “Instead of plans to criminalise people for seeking safety, the Government should be opening up safer routes for those seeking asylum – not raising the drawbridge and driving vulnerable people further into the hands of people smugglers.”

Jon Featonby, from the British Red Cross, said the figures confirm “changes to the asylum system are urgently needed” but he warned the Bill “will only make things worse”.

November 2021 saw the highest number of small boat arrivals in the last four years (6,971) and the number coming to the UK in each month of last year was higher than comparable periods in 2020.

Most of the people who made the crossing last year (90%) were male, according to the Home Office data.

Three-quarters (75%) of all arrivals were men aged 18 to 39, 5% were men aged 40 and over, while 7% were women. Around 12% were children, of which 76% were boys.

Some 30% of the people arriving were Iranian nationals, 21% were Iraqi, 11% were Eritrean and 9% were Syrian.

Iranians “represented the vast majority” of small boat arrivals in 2018 (80%) and 2019 (66%). But a greater mix of nationalities have been recorded since 2020, the Home Office said.

Information on gender and nationality was not available for some arrivals.

There was an average of 28 people on board each boat in 2021 and crossings took place around two in every five days.

There were 1,034 small boats (carrying multiple people) detected arriving in the UK in 2021, compared to 641 in 2020, 164 in 2019 and 43 in 2018.

The average number of people on board small boats last year was “much higher” than in 2020, when there were 13. This is compared to 11 in 2019 and seven a year earlier.

The Home Office document described small boat arrivals as a “phenomenon that was rare prior to 2019 but has since increased sharply in number” and made clear this method of travel is only one of a number which could be used to reach the UK border and “seek entry without permission”.

It added: “It is not possible to know the exact size of the irregular population in the UK, nor the total number of people who enter the UK irregularly.”

Dr Peter Walsh, senior researcher at the Migration Observatory at the University of Oxford, said the reasons for the rise in small boat arrivals “are not yet fully known” and it is “hard to predict how the numbers will change… over time”.

Immigration minister Kevin Foster said: “This Government is fixing our country’s approach to illegal entry to the UK and asylum by making the tough decisions to end the overt exploitation of our laws and UK taxpayers.

“We know there is no simple solution to this problem but our New Plan for Immigration will deliver the fair but firm system the British people have repeatedly voted for.”