Labour experts say a deposit is considered a work-finding fee, which is illegal in the UK and Indonesia.
One worker told the Guardian he made a #1,000 down payment in July to a Jakarta agency to guarantee an agricultural job with a British recruiter, but he had not even had a job interview.
He said he was one of several people left unemployed and out of pocket on the hope of a farm job in the UK.
"We stopped working to be able to seriously follow the recruitment process for a new and better job. Now we are unemployed and our fate is increasingly unclear," he said.
Official Indonesian government documents from late August suggest about 170 workers were stranded in Indonesia having been assigned jobs on 19 farms across the UK.
Most have been unemployed for several months, waiting for jobs they believed were imminent, and almost all have been given visas to come to the UK.
It is understood there are plans to bring some of these workers to Britain, despite it being so far into the harvest season.
It follows revelations in the Guardian that Indonesian labourers harvesting berries on a farm that supplies Marks & Spencer, Waitrose, Sainsbury's and Tesco had reported facing thousands of pounds in charges from unlicensed brokers in Bali to work for a single season in the UK. Brexit and the war in Ukraine have pushed desperate recruiters and farms to search for labour thousands of miles away.
A presidential taskforce in Indonesia is investigating the circumstances of the recruitment of fruit pickers after experts said the high fees alleged could leave workers at risk of debt bondage.
The Gangmasters and Labour Abuse Authority is investigating whether any UK laws were broken.
Andy Hall, an independent migrant rights specialist who investigates issues of forced labour in supply chains in Asia, said: "There is no legal basis either under Indonesian or UK laws to charge money to workers as a recruitment fee, whether it's called a deposit or not. At the time a deposit is taken from a candidate, it's an illegal recruitment fee."
He said the risks of debt bondage leading to forced labour and the involuntary departure of a worker overseas against their will would increase significantly if deposits were taken from workers rather than prospective employers or clients.
The Indonesian workers already in Britain were supplied by AG Recruitment, one of four UK agencies licensed to recruit using seasonal worker visas. AG denied any wrongdoing and said it knew nothing about Indonesian brokers charging fees or deposits.
AG had no previous experience in Indonesia and sought help from Jakarta-based Al Zubara Manpower, which in turn went to brokers on other islands who charged exorbitant fees to the people they introduced, according to one Al Zubara agent.
So far, more than 1,200 Indonesians have been placed on British farms this year by AG working alongside Al Zubara, the Guardian has learned.
Of these, 207 came from Bali, where Al Zubara has no office and relies on brokers to supply candidates. A further 102 are from Lombok, where the reliance on brokers is understood to be similar.
The managing director of AG Recruitment, Douglas Amesz, said AG only went to Al Zubara for help with advertising and to establish the demand letter, which gives formal permission to recruit workers.
But adverts seen by the Guardian give Al Zubara email addresses for applications, and under local laws only an Indonesian-licensed manpower agency can recruit. Local official paperwork suggests Al Zubara undertook the recruitment, though Amesz strongly denies this.
Now an Indonesian government source says workers report Al Zubara encouraging them to pay deposits of up to 50m rupiahs (#2,500) to guarantee a job in the UK. Many are understood to be waiting to speak to AG.
One worker who had not yet been interviewed by AG or signed a contract said he had been encouraged by Al Zubara to make a down payment of about #1,000 to show his interest and guarantee a job in Britain.
He said he knew others who had done the same, and the Guardian has seen receipts for two such payments. "We know that plenty of candidates are crying every day, waiting for news from AG," he said.
Amesz said: "The making of any form of payment, termed as a deposit or otherwise, to Al Zubara (AZ), or any party, in the form of a work finding fee is illegal both in the UK and in Indonesia and is not condoned by AG in any way. Our contracts with AZ specifically make clear that no such practices would be tolerated, and that AZ is to abide by local and English law. We also made clear to each worker directly, when I conducted the recruitment in Indonesia, that they should never pay for a UK job and to report any such approaches."
Al Zubara charges #2,500 for farm jobs in the UK, according to documents seen by the Guardian. The fees include flights and visas. Multiple labourers said they faced thousands of pounds in extra charges from Indonesian brokers who brought them to Al Zubara and promised substantial earnings. Al Zubara has been contacted numerous times for comment.
David Camp, the chair of the Association of Labour Providers, of which AG is a member, said: "The GLAA's responsibility is to conduct a full investigation and determine whether or not Al Zubara was supplying workers to AG. Al Zubara has no GLAA licence and it is a criminal offence to operate as a gangmaster without a licence or enter into arrangements for the supply of workers with an unlicensed gangmaster."
AG has strongly denied any suggestion that AZ was contracted to recruit for AG. Amesz said he did the recruiting directly in Indonesia, and that "AZ were contracted by AG to carry out services in Indonesia to help us establish the demand letter (for the work pathway) and subsequently to provide local advertising via job boards. The contracts with AZ specifically made clear that they were not to subcontract the work to third parties, nor were they to apply charges to the workers."
AG blamed Indonesian bureaucracy for delaying the allocation of work permits. Al Zubara had its licence to recruit to the UK temporarily suspended in the week after the Guardian published its first story.
AG had been intending to hire from Ukraine before war broke out and had to scramble for large numbers of workers in a new market at short notice.
Amesz said AG was aware of workers in Indonesia waiting to come to the UK and he had interviewed "all remaining workers to establish their individual circumstances". He said he had interviewed candidates still in Indonesia about "what, if any, payments the workers have made and to who".
Andrew Opie, the director of food and sustainability at the British Retail Consortium, said: "Our members are aware of these allegations and remain extremely concerned. They are urgently investigating possible breaches of the scheme with suppliers.
"It is clear recruiting seasonal workers has become more challenging, particularly with the loss of Ukrainian workers, and retailers will work in partnership with farmers, scheme operators, enforcers and the government this autumn to ensure all labour rights continue to be protected."
A Tesco spokesperson said the supermarket welcomed investigations in both countries, and it was "vital that any illegal fees are repaid in full".