Priti Patel has come under fire from the borders watchdog for stalling for months on publishing a report into the number of asylum seekers making the perilous Channel crossing.
Chief Inspector on Borders and Immigration David Neal expressed frustration at the Home Secretary for sitting on his independent report into the small boats crisis since February.
In an unusual public rebuke, he suggested officials were delaying publication out of "concern about the tone" of his comments - and accused the Home Office for undermining his independence.
Shadow Home Secretary Yvette Cooper branded the delay "completely reckless" - and accused Ms Patel of coming up with "gimmicks and unworkable plans" rather than solving the crisis.
It comes as new figures show more than 15,000 migrants have arrived in the UK so far this year after crossing the Channel in small boats.
Ms Patel has come under intense pressure from Tory MPs to get to grips with the numbers of desperate people crossing the busy shipping lane in dinghies.
But her plan to deter arrivals by sending asylum seekers arriving in Britain illegally to Rwanda has stalled after legal challenges.
Mr Neal submitted his report on small boat crossings in February and it was due to be published within eight weeks.
But it still hasn't emerged with days to go until the summer recess.
Mr Neal said: "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.
"My report made 4 recommendations, all of which were time bound. The 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."
It comes after Ms Patel enraged MPs by refusing to attend a grilling over her job and controversial policies - like deporting migrants to Rwanda last week.
The Home Secretary skipped a hearing of the Home Affairs Committee in Parliament with only hours to go - after her attempt to bid for the Tory leadership fell through.
Ms Cooper said: "This is completely reckless from the Home Office. They should be doing everything possible to crack down on criminal gangs and combat these dangerous channel crossings.
"For Conservative Ministers to refuse to publish or respond to proposals from the Independent Inspector to tackle channel crossings is completely irresponsible and shows they are not serious about tackling this serious problem.
"The Inspector’s statement comes just weeks after it was revealed that the Home Secretary had failed to meet with him in more than a year.
“A serious Home Office would do everything possible to combat these crossings, but all we get from Priti Patel is gimmicks and unworkable plans."
A Home Office spokesperson said: "We thank Mr Neal for his report which will be laid before Parliament this week.
"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."
