In a statement National Express said Mr Patterson, who joined in August after serving as a director of the BET conglomerate until its takeover by Rentokil last year, had relinquished his role as chief executive by "mutual agreement" with immediate effect.
But sources close to the company acknowledged that Mr Patterson's appointment had been a mistake. "Both sides felt it wasn't the right company for him," said one. "There were big cultural differences between BET and National Express."
Colin Child, finance director, said both parties agreed that Mr Patterson "was not suited to National Express and National Express was not suited to him". But Mr Child stressed: "There was no dispute at all; no fight or debate or difference of opinion on commercial or strategic issues at all."
Nevertheless, the resignation took insiders at the company and the stock market by surprise. "There was no hint of this," said a senior manager just below board level.
Shares in National Express were as low as 526.5p at one stage, but they recovered to close 3.5p lower at 540.5p in a rising stock market.
Mr Patterson, who has been replaced by Phil White, formerly director of the West Midlands Travel unit, was on a one-year contract which will be honoured in full. The size of his pay-off remains unclear because details of his salary were never made public. His predecessor, Ray McEnhill, was paid pounds 411,000 in 1995, up from pounds 327,000 in the previous year.
Mr Child said that "cultural style differences" had emerged between Mr Patterson and National Express. "The style and approach of a big group with a smaller, rapidly growing group is very different," he said.
National Express had a more devolved management structure than Mr Patterson was used to, Mr Child said.
Mr Patterson had been responsible for BET's world-wide transport interests, including road tankers, containers, warehousing and distribution.
Analysts believed his appointment heralded a subtle shift in focus away from the UK, where buying opportunities in the core bus and coach market were becoming increasingly hard to come by.
Instead Mr Patterson committed National Express to bidding for all 12 remaining rail franchises after landing the Gatwick Express and Midland Main Line licences. National Express is also interested in buying the Welcome Break motorway service stations from Granada, the media and leisure conglomerate. The coach group also owns East Midlands airport and is seeking links with airlines to provide dedicated airport services.
Mr White joined West Midlands Travel in 1994 and became a director of National Express in January 1996. He will continue to have day-to-day responsibility for WMT until the appointment of a new managing director at WMT.
In an update on trading,Michael Davies, the chairman, said: "Although the 1996 financial results are not yet available I can confirm that based on our latest estimates the group has traded well across all its divisions in the second half of 1996 and looks forward to 1997 with confidence."
The group remained committed to the expansion and development of its businesses and to acquisitions in existing and related areas, he said.