ICS technology opened up the prospect of putting cask-conditioned beers into cans. Experts estimated that by the end of the century half the cans consumed in British homes would have bits of plastic inside them.
The plastic rings in cans of Draught Guinness cause nitrogen and carbon dioxide to form bubbles in the stout which give it a creamy head.
Guinness Brewing Worldwide launched the can three years ago and has since sold 200 million units. In 1991 came Guinness Draught Bitter.
Most of the big brewers have followed, treading carefully around the patents Guinness placed on its invention.
Among the many drinkers converted to the new cans was Duncan Thorburn, 34, a miner from Nottingham. On 30 October, his mother bought him eight cans of Guinness bitter - complete with widget - and four of the draught stout.
'As I was about to take my last drink of Draught Guinness, I noticed something unusual in the glass: some very sharp hard- ridged plastic fragments.'
He opened a second can and this too produced fragments. A third revealed a fractured plastic insert, which had not broken into pieces. He noticed the cans were bulging outwards instead of inwards at their base.
Several days later, Mr Thorburn noticed a tickle at the back of his throat. He feared that he might have swallowed a fragment and went to the doctor. At a local hospital he was told it was not possible for a proper diagnosis to be made because the fragments are invisible to X-rays. He still has the tickle.
Mr Thorburn contacted Guinness Brewing Worldwide in London. On 3 November, he sent the faulty cans to Guinness by recorded delivery.
The following day he received a call from the quality inquiries manager, Tim Powlesland. He was told that no similar complaint had been made before and that he would have to wait up to 10 days for an explanation.
By 24 November, Guinness had still not concluded its investigation. 'I was really angry. I said there was no explanation for them not taking the stuff off the shelves or warning people.'
Mr Powlesland then visited Mr Thorburn at his home. He explained that the decision not to issue a warning was taken at board level.
Mr Thorburn was then referred to the Guinness company secretary, Brian Beanland. A week before Christmas, Mr Beanland told Mr Thorburn that the company still had no firm idea what was causing the damage. He indicated that it was probably caused before the cans arrived in the shops. It also became clear that the company had received other complaints of a similar nature. There were at least three after Mr Thorburn first contacted Guinness. One woman had reported fragments in her mouth but had not swallowed them.
Mr Beanland emphasised that no injuries had been reported. He told Mr Thorburn that the company doctor had advised that fragments could be harmful to children, but probably not to adults. 'I think we all have to acknowledge that medical opinion will vary. We're not complacent and I'm not saying that there are no circumstances (when it could do harm).'
Mr Beanland insisted that there were unlikely to be any other problems because when the widget broke the beer poured flat and that ordinary drinkers were unlikely to drink flat beer.
Mr Powlesland went on to explain that a special project team had been set up to examine the problem but said he could not go into the details of their research. He said that Guinness had chosen not to inform the public health or trading standards authorities because 'we're taking all the actions that we believe are necessary anyway'.
None of this has satisfied Mr Thorburn who believes that there are possible dangers. He is particularly concerned that Guinness has taken so long to investigate the cases it is aware of. Bass withdrew cans of Draught Worthington's Best Bitter from sale on Sunday after three reported incidents in which plastic was found in the beer.
Bill Spears, public affairs director at Guinness, said the Bass carbonation system was different to that of Guinness, and that the situations were not comparable. 'One has to bear in mind the number of cans. All food firms from time to time have a product that is less than 100 per cent.'
He ruled out any recall for the product, which has cost more than pounds 40m to invent and promote.