In 1983 he was back for a full season on a factory Honda as teammate with American Freddie Spencer. He raced in the 500 class from then until the end of the 1990 season, spending three years developing the experimental Elf Honda race bike with its single-sided swinging arm front and rear suspension.
Haslam was a member of the British team in the then-annual Transatlantic Match Races between Britain and the USA. Haslam was at his best in the 1983, ending the three-day meeting as overall top points-scorer. In the opening round at Oulton Park on the Good Friday, Haslam was beaten to the finish line by Randy Mamola in the first of two, 11 lap races. Haslam, on the Honda NS500, equalled the lap record as he strove to beat the American. In race two Mamola again came out on top, with both riders this time sharing the fastest lap, which was one tenth of a second off the record. At that point, Britain led 79 points to 69. At Snetterton two days later Haslam notched-up victories in the rain, chased home each time by Kenny Roberts. Britain's lead had grown to 28 points, 161 to 133. In the dry at Brands Hatch the following day Haslam again won both team races to lead Britain to a 245 to 198 victory. Haslam had scored 70 points of his team's total, 15 more than Roger Marshall and 30 better than the next best, Barry Sheene. The Langley Mill racer was the highest British points-scorer again in 1984, on a standard road-going Honda VFR750 in the series in 1986, on which he took two-thirds at Donington Park.