Amey also has the option to buy the remaining 49% stake by 2003 for a maximum price of £67.5m. The exact figure will depend on the company's growth. Amey said the price had been set high as an incentive to Crown management and staff.
Crown provides media, technology, communication and consultancy services. It specialises in producing annual general meetings.
Amey chief executive Brian Staples said Crown's services complemented Amey's own and that the business would be placed in the group's technology services division.
He said: "It fits perfectly with our other business solutions operations and will allow us to further enhance our broad combination of services to the marketplace."
Crown's turnover last year was £13.9m. It made a loss of £1.6m as a result of spending on new technology.
