One of Britain's wealthiest businessmen is facing jail after being found guilty of making a large corrupt payment to Saddam Hussein's regime in a "shady" deal.

David Mabey, 49, and a colleague, Charles Forsyth, 62, have been convicted at Southwark crown court in London. Mabey's family has made an estimated £200m fortune from selling steel bridges around the globe.

His bridge-building firm, Mabey & Johnson, was the first major British company to be convicted of foreign bribery after admitting in 2009 to systematically paying bribes in Iraq and many other countries to win contracts.

After securing a corporate conviction of the family firm two years ago, the Serious Fraud Office moved on to prosecute Mabey himself and two employees of the company for making illegal payments to Saddam's regime.

The trio, who could face up to seven years in jail, will be sentenced on 23 February. One of them, Richard Gledhill, 64, the firm's former sales manager for Iraq, admitted his guilt over the payments last year and gave evidence for the prosecution during the trial.

The court was told that the three men conspired to bump up the price of a contract to build 13 bridges in Iraq by 10% of its value so that kickbacks worth more than £365,000 could be delivered to the Iraqi government a decade ago.

The Iraqi regime had devised the kickback system to bypass the oil-for-food programme that had been imposed on the country by the United Nations to ensure that the country's needy received vital food and medicines. Peter Blair QC, counsel for the SFO, said: "This is something the United Nations sanctions specifically prohibited and which English law specifically prohibited."

A UN investigation has claimed that more than 2,000 firms around the world broke these sanctions. For Reading-based Mabey & Johnson, the contract was a way back into a potentially lucrative market. Blair added that it was a "shady deal" authorised by Mabey, who lives in Maidenhead, Berkshire, and Forsyth, of Butts Meadow in Hampshire, then the firm's managing director.

During the trial, the prosecutor showed the jury documents which he said demonstrated that "a bit of hard bargaining was going on" by Mabey.

Mabey took over the running of the firm from his father Bevil, who built up the business having started out buying army-surplus portable Bailey bridges after the second world war.

Allegations of corruption surfaced in 2005 after a Guardian investigation into the firm's contractual dealings in the Philippines and Papua New Guinea. In 2009, the firm paid penalties of more than £6.5m after admitting paying bribes to politicians and officials in Ghana, Jamaica, Angola, Madagascar, Mozambique and Bangladesh.

Many of its exports have been backed by the British taxpayer through loans guaranteed by the Export Credits Guarantee Department.