The Home Office has come under fire over delays in publishing a watchdog’s report into migrant crossings as the number to reach the UK so far this year hit 15,000.

The Chief Inspector of Borders and Immigration David Neal said he was “increasingly frustrated” that the department had been sitting on his findings for months as he suggested concerns from officials about the “tone” of some of his remarks could be partly behind this.

The Home Office later said the report would be published this week.

Since the start of 2022, 15,107 people have reached the UK after navigating busy shipping lanes from France in small boats such as dinghies, according to provisional Government figures.

The milestone – almost double the number recorded this time last year (7,735) – was reached as it emerged the Foreign Office had advised against the Government sending migrants to Rwanda over human rights concerns.

Mr Neal, who was appointed by Home Secretary Priti Patel to the role in March last year, is the latest immigration watchdog to raise long-standing concerns over her department’s delays in publishing reports, and argued there was a “strong public interest” in the findings.

The report, now expected to be made public on Thursday, scrutinises how migrants are initially processed once they arrive on the Kent coast.

The document was submitted to Ms Patel in February and should have been published by the end of April, Mr Neal said, adding: “I have spoken with senior officials at the Home Office, and I do not think that there is any disagreement with the content of the report or the recommendations. I understand they have some concern about the tone of my foreword, and I suspect this is part of the reason for the delay.”

The recommendations made are “timebound” and “failure to publish within the period suggested begins to devalue the purpose of independent oversight, and continued failure to publish such an important report infringes on my independence”, he warned.

The watchdog previously told MPs the Home Office was operating under “constant crisis mode” and described its leadership as a “big issue”, adding that the department “routinely” breached agreements to publish reports within eight weeks.

The Home Office thanked Mr Neal for his report but would not explain the delays in publishing. A spokesman added: “It is right and proper for the Government to take time and fully consider recommendations suggested in independent reports before agreeing to make changes to policies.”

Migrant crossings continued on Monday for the 11th day in a row, with 330 people including babies braving the heatwave in seven boats, Ministry of Defence (MoD) figures show.

More than 2,000 people arrived in the UK between July 8 and July 18, the longest consecutive run of crossings to date this year.

The highest daily total so far in 2022 was recorded on April 13 when 651 people made the crossing in 18 boats.

The following day Ms Patel signed what she described as a “world-first” agreement to send migrants deemed to have arrived in the UK “illegally” to Rwanda. Since then 9,839 migrants have crossed the Channel.

The High Court was told on Tuesday documents revealed the east African nation had initially been excluded from the shortlist of potential countries for the policy on “human rights grounds” and memos detailed how Foreign Office officials had advised Downing Street against engagement with Rwanda, among other countries.

Another official memo, dated shortly before the UK-Rwanda deal was announced, warned “fraud risk is very high” and that there is “limited evidence about whether these proposals will be a sufficient deterrent for those seeking to enter the UK illegally”.

Several asylum seekers, the Public and Commercial Services union (PCS) and charities Care4Calais, Detention Action and Asylum Aid are challenging the legality of the Home Office policy, with another court hearing due in September.

Meanwhile the All-Party Parliamentary Group (APPG) on Immigration Detention heard there were fears the Rwanda plan would “exacerbate” dangerous people smuggling operations and that no further removal flights had so far been scheduled since the first attempt was grounded in June amid legal challenges.

Andrew Leak, from the UN’s refugee agency the UNHCR, told the committee: “We understand that the UK Government has released some individuals from detention and we welcome these decisions. And we also understand that some asylum seekers have sought to review of the legality of that detention.”

Organisation Medical Justice said more than half of the 40 migrants facing removal that it had been supporting have now been freed from detention after they were granted bail at tribunal hearings.

Also on Tuesday, the Home Office said it had deported 14 foreign criminals to Poland.

Last week, Ms Patel pulled out of being questioned by MPs and then declined requests by the Commons Home Affairs Committee – which has warned there is “no evidence” the Rwanda policy is acting as a deterrent – to appear in front of them on Wednesday before Parliament’s summer recess.