Qatar's former Fifa vice-president Mohamed bin Hammam has come under fresh scrutiny over claims he used his top level contacts in the Qatari royal family and government to arrange deals and favours to secure the World Cup for his country.

The Sunday Times reported that it has seen documents that appear to undermine the Qatar 2022 committee's claims that Bin Hammam had no "official or unofficial role" in its bid.

The latest revelations have increased pressure on Fifa, football's world governing body, to take action as one of the tournament's biggest sponsors, the Japanese electronics giant Sony, called for the claims of wrongdoing during the bidding process to be "investigated appropriately".

Ed Miliband, the Labour leader, has said that if the leaked documents disclose the truth there would be an "overwhelming case for the bidding process to be reopened immediately". The latest revelations include the claim that Bin Hammam brokered government-level talks through the Thai member of Fifa's executive committee (Exco) to push a gas deal that was potentially worth tens of millions of dollars to Thailand.

Another allegation is that he was invited to visit Vladimir Putin to discuss "bilateral relations" in sport between Russia and Qatar a month before the World Cup vote took place in December 2010, which resulted in their landslide victories to stage the tournament in 2018 and 2022 respectively.

They also allege that the disgraced Qatari official arranged for Michel Platini, the Uefa football chief and an Exco member, to meet the Qatari bid committee and that he arranged discreet meetings with members of the Qatari royal family for at least seven key Exco members, including the Fifa president, Sepp Blatter. Another allegation is that Bin Hammam used secret slush funds to make payments totalling $1.7m to football officials across Asia.

An Exco meeting between Blatter, Platini and others broke up on Saturday night with further refusal to comment on the Bin Hammam allegations.

Michael Garcia, Fifa's in-house investigator, last week announced that he would cut short his investigation into corruption in the World Cup bidding process ahead of Fifa's congress in São Paulo on Tuesday without reviewing the fresh evidence.

Miliband said: "Few people will have much confidence in the investigation being conducted by Fifa unless it takes full account of the evidence uncovered by the Sunday Times."

He said the Fifa files contained "startling evidence that the decision to make Qatar the host for the World Cup in 2022 may have been corrupted".

The newspaper alleges that the files "lay bare" the degree to which Bin Hammam could use his connections to get key football figures to meet the emir, the crown prince and other senior royals as part of the campaign to generate support for Qatar's bid.

It states: "The files show that Bin Hammam was fixing the meetings for members of Qatar's ruling family with football's most powerful men at the same time as using a network of secret slush funds to buy up a groundswell of support among the bosses of national football associations."

The Qatar bid committee denies any wrongdoing.