Young, foolish, but not criminal: Sarah Wilson is serving 12 years for importing drugs she didn't know she was carrying. The man who planted them got just eight years.

It isn't quite Perseus rescuing Andromeda, or Lancelot pulling Guinevere from the flames; but Karl Wheeler, 29, from Hampshire, has rather belatedly come to his own kind of gallantry. He is trying to get an innocent woman, Sarah Wilson, the mother of a seven-year-old boy, released from a 12-year sentence in Winchester prison. The only trouble is that he put her there in the first place.

Sarah Wilson, now 25, was born in Farnborough, the youngest daughter of Janet and Ron Wilson. They lived on the shining new Prospect estate, and Sarah went to school down the road. When Sarah was nine, her parents divorced. But Janet remarried, and the girls moved in with her and George Daly. They didn't travel far. Like her sisters, Sarah went to Oak Farm Comprehensive. She didn't like it - preferring loud reggae and dancing to homework - and couldn't wait to leave. At 16, armed with a scattering of GCSEs, she landed a job at Boots. That's when she met Wheeler, who'd been at Oak Farm in her sister Angie's year, and in trouble with the law for offences which included possession of cannabis.

Within a few months, she became pregnant. Wheeler attended the birth, if only reluctantly. Waiting for a council flat, Sarah and baby Aaron lived in bed-and-breakfasts until they were given a two-bed, groundfloor flat in Perrin Avenue, a mile from Sarah's parents. Wheeler stayed away. "He treated us badly," recalls Sarah. "He was never there for Aaron. He only came round every couple of months and he didn't pay maintenance. We'd argue a lot but I still loved him."

After Aaron started at school, Sarah worked in a sports shop in the local shopping centre - and in a pub - but last year the Child Support Agency wrote to Wheeler demanding £8,000. Outraged, he stormed round to Sarah's, denying paternity and demanding a DNA test.

Within weeks he apologised, promising to "make things up" and offering to take them on holiday. "I assured her I wanted to get closer to Aaron," he later said. Sarah was suspicious. "It was out of the blue." She asked if he meant to smuggle drugs. He said: "Don't be so stupid, I wouldn't get you or Aaron involved." If he was going to do that, he said, he could ask plenty of other people. (In fact, Wheeler had asked two other girlfriends, but they'd turned him down.) "I knew Sarah would accept," he later said, "because she was always madly in love with me and always wanted us to be a proper family." He was right. Sarah agreed to go. Wheeler booked the holiday, but kept the destination secret till they reached the airport, on Tuesday 10 June 1997.

At the Flamingo Beach Hotel in Margarita - an island off Venezuela - everything was included in the price: food and drink, cabarets, and games by the poolside with bottles of rum for prizes.

On the last day, Sarah and Aaron had left Wheeler asleep upstairs to go to the pool. When they saw him again (around 4pm) he claimed to have been asleep all day. But that didn't explain his new bags. Spotting these - two on the bed, one on the floor - Sarah was appalled. "We had a huge row," she says, "and he told me he was taking the cases back to England for a friend." Again she asked about drugs - but again he reassured her, swearing repeatedly that nothing was wrong.

Just to be sure, Sarah inspected the cases: "I unzipped and looked inside each one, and eventually I thought there was nothing wrong with them." Then Wheeler played his ace: "He swore - on Aaron's life - there were no drugs," says Sarah. "And I believed him." Foolish? Perhaps, but that's not a crime.

On Wednesday 25 June they arrived at Gatwick. From Gate 22, Wheeler went to make some calls, leaving Sarah with Aaron and the luggage. After a long flight and some hours' delay, they were tired. Rather than go straight home, Wheeler took them to a nearby hotel, checked in, and left them to make more calls. Then he woke them up and announced they were going home.

At 6.55pm, on the M25 near Dorking, their taxi was stopped. Customs officers had detected drugs in the bags as they came off the plane, and set police on the trail. Now, searching inside the bags' false bottoms - which could be opened only with a screwdriver - they found nearly 12 kilos of cocaine, worth £1.25 million.

Sarah's sister Angie was summoned to collect Aaron from Gatwick. Sarah and Wheeler were charged under Section 3(1) of the Misuse of Drugs Act. Sarah was imprisoned on remand in Holloway, till December, then bailed until the trial began, in February, at Croydon Crown Court.

Wheeler had confessed. He was part of a gang, he'd been promised £3,000 for each kilo he brought back. Sarah and Aaron, he explained - as a witness for the prosecution - had provided useful cover, but they knew nothing about it.

Apart from Sarah, there were three men in the dock, accused of playing various roles. Their presence would complicate matters. One claimed an alibi, another said he was acting under duress. Sarah just said she didn't know about the drugs, and wouldn't have travelled if she had known. Half-way through the trial, the prosecution accepted that she had indeed known nothing before leaving England. They still said she must have found out in Margarita and had, therefore, "knowingly" imported the drugs.

But Sarah was confident she'd be acquitted. On 23 March this year the jury reached a verdict by a majority often to two. Guilty. Sarah became hysterical. "My breathing went funny," she says. "I said to them,' I'm innocent'." Two of the jurors, both women, were in tears. The others looked away.

His Honour Judge Simon Pratt said the guideline sentence for importing such a quantity of cocaine was more than 15 years.

But "you were put in something of a dilemma by Wheeler and to an extent must have been an unwilling partner . . . this reduces the sentence below that which I should otherwise have been forced to impose." He gave her 12 years. Wheeler, presumably because he pleaded guilty, got a sentence of only eight-and-a-half years.

Sarah's MP, the Conservative Gerald Howarth, describes it as "a serious miscarriage of justice" and has written to the Attorney General requesting a speedy appeal. He recently received a letter from the solicitors' office of Customs & Excise. It said: "Given her [Sarah's] limited role, we do accept that the sentence of 12 years is more than we would have expected." This, says the campaigning journalist Paul Foot, is "a very rare example of the prosecuting authority criticising a judge's sentence for being too long".

Foot adds: "Even if she suspected something, her offence was infinitely less grave than that of Wheeler. She was absolutely trapped, out there with her child. This is monstrous judicial barbarity. Every single member of the jury must have been horrified by the sentence."

Her supporters include the former Law Society president Martin Meats, hardly, as he puts it himself, a "bleeding-heart liberal". He argues that the summing-up was inadequate. Judge Pratt spoke for a whole day which, in a case with four defendants, could easily muddle the jurors. And he still omitted important points, say Sarah's supporters. However much Sarah distrusted Wheeler's explanations, what was she supposed to do: tell the Venezuelan police that the father of her son might, just possibly, be up to something?

Now Aaron is being brought up by Sarah's mother and stepfather. He is taken to visit his mother occasionally, when he describes the football trophies he's won at school or recalls the games round the pool during that ill-fated holiday in Margarita.

Wheeler, now serving his sentence in Kent, has written to Sarah, claiming that he will refuse to give prosecution evidence in another drugs case unless something is done about her sentence. He has also written a letter to Howarth: "I cannot live with this guilt. Sarah Wilson was sent to prison for something she knew nothing about . . . a good mother has been found guilty for something I done." And in a somewhat ironic phrase, he concludes: "Sir, please look into this case."