Unclear who authorises payments, which could total millions of pounds but do not appear in Home Office's annual report

The Home Office is making "secret" payments to embassies to provide travel documents for migrants they want to remove from Britain, the Guardian has learned.

The payments, which could amount to millions of pounds in total, do not appear in the department's annual report, and a spokesperson could not say who authorises them or which budget the money comes from.

Diplomatic sources from embassies in Asia, Africa and the Middle East described how the money was offered in return for providing travel documents as quickly as possible.

Many asylum seekers and other migrants arrive in Britain without their passports, and they cannot be removed without travel documents. About 60,000 people were removed from the UK last year, and the government has pledged to limit immigration to tens of thousands.

One diplomat from an embassy in Africa said: "I am under a lot of pressure from the Home Office to provide travel documents. I receive emails from officials about once every two days.

"I know that some embassies do accept payments from the Home Office for providing travel documents, but we do not because we consider it to be improper to take money for this. Sometimes it takes us a long time to check out whether someone the Home Office wants to remove is actually from my country."

The Home Office said it would not pay more than a three-figure sum for travel documents, and that the amount depended on what embassies asked for, but some diplomats said they had been offered substantially more.

In 2008, the German magazine Spiegel reported that the Berlin was paying Nigerian embassy officials €500 per person to issue travel documents for people they wanted to remove.

A Home Office spokesman said: "We work closely with embassies from a wide range of countries to obtain travel documents to assist removal."

The Labour MP Jeremy Corbyn has tabled questions in parliament about the secrecy surrounding the Home Office payments and asking for more information about them.

A Freedom of Information (FoI) request from the Guardian about payments the Home Office made to the Nigerian embassy confirmed that the department holds the information, but officials rejected the request to reveal it.

The response to the FoI states that disclosing the information would provide transparency about the level of co-operation between the Home Office and the Nigerian authorities, but that doing so could influence future agreements and negotiations between the two countries.

One asylum seeker said he had appealed to a contact at his country's embassy not to provide the travel document the Home Office had requested for him, as he feared for his life if forced to return home.

"My contact told me there was nothing he could do to help me because there is an agreement between the Home Office and the embassy that they are paid large sums of money for issuing travel documents," he said.

There have also been cases when people have been documented and removed to countries other than their own.

In one case, a Zimbabwean asylum seeker received an apology and substantial compensation from the Home Office, which wrongly tried to return him to South Africa.

In another case, the Home Office repeatedly tried to send a stateless asylum seeker to an eastern European country. The case went on for eight years and when he was finally granted refugee status last year, the judges in the case branded the Home Office's behaviour a public disgrace. A Home Office spokesman said: "We only pursue a removal and seek documents from a country if we believe the individual is a national of that country."

Corbyn said: "It sounds odd on two grounds. Firstly why the secrecy and secondly what effect does this have on the potential deportee in that their details would have been flagged up in advance to the authorities in the country concerned?"