The fee is pounds 5m more than the club's previous record and the club's owner, Sam Hamman, said: "This shows we are ambitious and can compete for the very best players. There is more money than ever in football now and we are determined that we won't be left behind."
Joe Kinnear, the Wimbledon manager, said: "I'm delighted. People may be surprised at the size of the fee but John has already proved he can score goals at the highest level and he is still only 23."
Many will indeed be surprised at the fee and Wimbledon's ability to pay it. Hartson signed for West Ham in a pounds 3m deal which had the potential to rise to pounds 5m two years ago and was an instant success, helping the club survive relegation that season, then leading the goal charts by Christmas 1997. But his form dropped alarmingly in 1998 and this season he has only managed four goals in all competitions. He has also been in trouble with the law and struggled with weight difficulties.
Hartson was also involved in an infamous training ground incident when he kicked his team-mate, Eyel Berkovic, in the head. Harry Redknapp, the West Ham manager, has alternately criticised and appeased the Welshman to no effect.
Wimbledon's ability to pay will be helped by the deal being spread, with pounds 3m paid immediately, another pounds 3m in a year's time, with a final million being performance related.
Redknapp may use the funds he has gained to try to buy Paul Merson from Aston Villa. The former Arsenal and Middlesbrough player has become disillusioned with Villa's manager, John Gregory.
Yesterday Merson urged Gregory to show him the same "leeway" as his Middlesbrough counterpart, Bryan Robson, did in his continuing struggle to stay off drink and drugs.
Merson warned that there were troubled times ahead if Villa failed to appreciate the extent of his endeavours to overcome addiction problems. The England player is furious at the "negative vibes" that greeted him at Villa after his weekend trip to New York. He admitted to being "depressed and down" in recent weeks, and that Gregory needed to recognise the importance of such breaks in his rehabilitation programme, as had Robson.
"What I did was right for me, given my circumstances. I had the weekend off and needed to get away. Villa knew I was feeling down, so I can't see what all the fuss was about," Merson said. "Bryan Robson was good as gold with such things. If I needed a few days off, to get away, then he would understand. Last season at Middlesbrough, when I was feeling down, he was going to send me to Tenerife for a week. I had the same sympathy from the managers when I was at Arsenal.
"If Villa want to get the best out of Paul Merson, then the same leeway needs to be shown. If the boss [Gregory] here, doesn't understand, then there are going to be problems."
Last night Gregory was believed to be locked in talks over the future of Merson. The Villa manager was understood to be meeting the player's agent, Steve Kutner.
It is believed that Gregory has been offended by the depth and extent of Merson's attack. The Villa manager may well be ready to sell him to West Ham sooner rather than later.
Arsenal will decide this week whether to buy Nwankwo Kanu for pounds 4.5m from Internazionale after putting the 22-year-old Nigerian striker through the sternest possible medical tests.
Kanu has been tracked by the Gunners' manager, Arsene Wenger, for months and the Frenchman's initial plan was to take him on loan for the rest of the season, after hesitating over a permanent signing because of the player's history of heart surgery and a current knee problem.
However, Kanu's Italian club, Inter, have insisted upon a full rather than a loan deal, at pounds 4.5m. Wenger said: "I'm hopeful the deal for Kanu will go through because he will be a big asset for us."Reuse content