Channel 4's Dispatches programme used undercover investigators to meet a mechanic from Doncaster-based Ecuflash, a software programming firm, and secretly filmed him.
Many British hauliers are using hi-tech devices and computerised hacking to disable emissons controls on vehicles, worsening air quality and saving firms money.
Experts say the premature deaths of 23,000 people each year in the UK are linked to the types of dangerous gases produced by HGV diesel engines, and the programme demonstrates how vehicles that have had their emissions systems modified produce far higher levels of dangerous pollutants.
In the programme, which will be aired tonight at 8pm, the Ecuflash employee is filmed telling investigators that it tajes 20 minutes to remove the lorry computer.
Once software had been tampered with it took another 20 minutes to reinstall.
‘It’s just a program that we put in the truck that turns it [the filter] off. It’s all plugged in and they’ll never know,’ he said.
Strict rules mean every diesel lorry over 3.5 tons must have a filter on its exhaust - but many firms desperate to cut costs are paying £700 a time to disable the device.
The investigation found numerous firms offering the disabling service on the internet.
Hauliers are tempted to break the law because faulty filters can cost £5,000 to fix. On top of that a lorry may be off the road for a week or two.
Last night, Ecuflash told the Daily Mail: ‘The “software” which we mention is to prevent the vehicle going into limp mode and causing a hazard on the road.
'This is all we offer to our UK customers now, unless the vehicle is going for export or being used off road.’