Analysts claimed the departure reflected Mr Lockyer's failure to secure the pounds 73m acquisition, which would have turned Triplex into the UK's biggest metals castings group and increased the group's earnings by 30 per cent.
The bid failure cost Triplex pounds 2.1m in legal and advisory expenses and depressed the company's share price. Andrew Cook, chairman of William Cook, defeated Triplex's hostile move in February by taking the company private through a pounds 80m management buyout.
While Colin Cooke, chairman of Triplex, maintained yesterday that Mr Lockyer's departure "had nothing to do with the bid ... and was over differences of opinion about strategic direction", analysts said the departure clearly reflected the damage to Triplex's reputation arising from the takeover fight.
In particular, analysts pointed to the leaks to the press during the bid of confidential information on William Cook which led to a public reprimand by the Takeover Panel. Mr Lockyer's departure comes a fortnight after the company dispensed with the services of Citigate, its public relations advisers for the takeover attempt.
One analyst said yesterday: "Mr Lockyer engineered this bid and must be responsible for how bitter it became. He also simply failed to nail William Cook. Buying that company would have transformed Triplex."
Analysts pointed out that Triplex's chairman had a reputation for toughness. John Foley, chief executive prior to Mr Lockyer, departed three years ago over a poor profits record. One analyst said: "Colin has a bit of a reputation as a hatchet man. Graham was a lovely person and well liked, but he wasn't the ideal one to lead on these decisions. It's probably a fair decision to let him go."
Bob Mitchell, finance director, is assuming the chief executive's role until a replacement is found. Mr Lockyer had been on a two-year rolling contract and earned pounds 252,000 last year.
Mr Cooke said the group would not make any more hostile bids, though with low gearing the company had around pounds 20m to spend on bolt-on acquisitions.
"I do regret this bid," he said. "The cost was heavy. It was going to give us substantial synergies and it was a very undervalued company. But if I could go back I would not do it again."
Though the bid has depressed Triplex's share price, which eased 1p to 154p yesterday and has fallen from more than 200p earlier this year, analysts were generally impressed with the group's results for the year to March and said the group looks undervalued.
The results, released yesterday, showed that taxable profits rose 19 per cent to pounds 11.3m and earnings per share by 25 per cent to 13p.
Paul Compton of Merrill Lynch said: "It is not many engineering companies which have just reported a 20 per cent rise in earnings and have no debt which are at half the value of the market."