An investigation has been launched into how unpaid workers bussed into London for the Diamond Jubilee celebrations were left stranded in the middle of the night.
The unpaid workers could get "restitution" as a result, the company responsible for providing the Government's Work Programme scheme in South West England said.
Prospects Group said it was launching the inquiry following allegations the jobseekers were forced to sleep in the cold under London Bridge before the Thames Pageant celebrations.
The firm said it was investigating the actions of employment charity Tomorrow's People, which was involved in organising the placements, and security firm Close Protection UK, which provided stewards at the Jubilee events.
A statement on the Prospects Group website said: "Following adverse press reports relating to the working conditions and supervision of a number of trainees over part of the bank holiday weekend, Prospects, as the prime contractor for the Work Programme in the South West, will carry out a full investigation to ascertain the facts and make recommendations for the future."
Prospects said the investigation will focus on "the management of the project, supervision arrangements over the weekend, the working conditions, health and safety issues and the quality of the work experience provided to the apprentices involved".
The firm added: "The intention is that, after ascertaining the facts, restitution may be made to affected clients if appropriate and lessons learned for the future.
"Prospects accepts its responsibilities as a prime contractor to ensure that everything possible is done to deliver programmes of the highest quality.
"We will do our utmost to learn from this experience."
According to reports, the jobseekers from South West England had to change into security gear in public and could not access a toilet for 24 hours.
After a 14-hour shift in the rain on Sunday - marshalling crowds who had turned up to watch the river pageant - they were then taken to a swamp-like campsite outside London, it is claimed.
But Molly Prince, managing director of Close Protection UK, said the situation had been "exaggerated".
Former deputy prime minister Lord Prescott condemned the "complete disregard" shown to the unpaid stewards.
The Labour peer, who has urged ministers to investigate, warned that the incident could set the tone for the treatment of workers during the Olympics.
Lord Prescott accused the government of exploiting cheap labour, saying: "It raises many questions on the provision of unpaid labour in these kind of positions, not only on the Jubilee event, but also particularly for the coming Olympic ones."
Ms Prince said there had been "logistical mistakes" but told Today: "We're talking about two or three people complaining out of 220 staff that were supplied to the event.
"It was badly handled and for that we've extensively apologised. We're not in the business of exploiting free labour."
She said the stewards had been left under London Bridge after their bus arrived there two hours earlier than scheduled.
A Downing Street spokeswoman described the incident as an isolated "one-off" and said that Close Protection had apologised.
The Number 10 spokeswoman said: "This is an isolated incident. The company itself has apologised.
"The Work Programme is about giving people who have often been out of the workplace for quite some time the chance to develo