Asylum seekers were subjected to excessive use of restraints after escort staff were given "dire" warnings about the potential for disruption on a removal flight, an inspection report found.
HM Inspectorate of Prisons said it had "serious concerns" after observing an operation to transport detainees to three European countries in January.
The assessment detailed how 80 staff accompanied 23 people from two immigration removal centres on a charter flight from the UK to France, Austria and Bulgaria.
All but one of those being removed were restrained in a waist belt, which restricts arm movements and can hold arms clamped to the body in the secure position.
HMIP said a staff briefing prior to the flight had "emphasised the risks of disruption and the need for vigilance", focusing solely on control and not on detainees' treatment or welfare.
One manager said: "Tonight we don't mess around. If you do, you may well get hurt."
The inspection report said: "Staff clearly thought they were dealing with a very high risk group. However, the dire warnings they were given were not grounded in evidence."
Home Office notes on detainees from Brook House Immigration Removal Centre (IRC), near Gatwick (pictured), stated that most had no history of being disruptive and presented "minor or no risk to successful transfer".
Detainees were placed "unnecessarily" in waist restraint belts and there was a "clear presumption" in favour of using the belts, according to the inspectorate.
It noted that eight detainees resisted attempts to remove them, leading to force being used on them.
Treatment of the asylum seekers was "reasonably courteous", but some staff were "flippant" and spoke to each other in "loud and jocular" voices, the report said.
Inspectors were particularly concerned that the only female on the flight was transferred in her pyjamas, slippers and dressing gown and a waist restraint belt, despite a lack of evidence that one was required or proportionate.
She was not offered clothing before disembarkation, other than a coat.
Chief Inspector of Prisons Peter Clarke said: "We regularly inspect other detention settings where far more disruptive and challenging behaviour is managed without such physical restraints.
"Clearly, some senior-level intervention is required to ensure that the situation is rectified without delay.
"We will inspect more removals over the coming year, and it would clearly be a matter of serious concern if those being removed from the United Kingdom continue to be subjected to unjustified use of force."
The UK is party to the Dublin Convention, an EU law that determines which member state is responsible for considering an asylum claim - and allows member states to transfer an asylum seeker to the responsible country.
The Home Office's Third Country Unit (TCU) manages such removals to and from the UK.
HMIP's report - its first to cover a TCU charter removal - is published at a time when the department's immigration procedures are under intense scrutiny following the Windrush scandal and controversy over removal targets.
A Home Office spokeswoman said: "The dignity and welfare of all those in our care is of the utmost importance and we are taking the concerns raised by the inspector in this troubling report extremely seriously."
She said action is already under way to address the recommendations, including the introduction of body-worn cameras under a new escorting contract.
"Any use of force must be justified and proportionate and used only as a last resort," the spokeswoman added.
Tascor, which is part of Capita, was the escort contractor for the flight, which took detainees to Toulouse, Vienna and Sophia.
A Capita spokeswoman said: "The dignity and welfare of people under escort was always of the utmost importance to Tascor, and any decision to use restraint was done on a case-by-case basis and in line with Home Office guidance.
"Although we can't comment on individual cases, any complaints received about employees would have been investigated thoroughly, and if employees had not met our standards, we undertook the appropriate action."
Copyright (c) Press Association Ltd. 2018, All Rights Reserved. Picture (c) Gareth Fuller / PA Wire.