Mark Lappin, the European boss of Dart Energy and the public face of its plan to exploit underground gas in Scotland, has resigned.

He left on Friday to take up a job with gas firm Centrica in Aberdeen, where he lives. His departure follows the stalling of Dart's planning applications to sink 22 wells at 14 sites to extract coal-bed methane at Airth, near Falkirk.

After prolonged delays by Falkirk and Stirling councils, and more than 1500 objections, Dart appealed to the Scottish Government last month for a decision. Both councils have urged ministers to hold a public inquiry.

Lappin joined Dart Energy in April 2012 as Europe general manager, responsible for progressing the company's flagship development at Airth. Before that he spent 16 years with the US oil giant, ExxonMobil, in Aberdeen, Texas and Germany.

His departure from Dart follows the loss of another senior manager, Lynne Campbell, four weeks ago. A further four staff have also left in the last two weeks. Dart is shedding 70% of its staff worldwide after the introduction of tough government regulations saw it withdraw from Australia, where the company has its registered office.

Critics said that Lappin's leaving is "another nail in the coffin" for the firm's plans in Europe.

Ed Pybus from campaign group Frack Off Scotland said: "Dart's development in Falkirk has been stalled, we hope permanently, due to overwhelming public opposition."

Dr Richard Dixon, director of Friends of the Earth Scotland, said: "Mark Lappin has deserted the sinking ship, obviously realising Dart's deeply unpopular proposal at Airth isn't going to make it through the planning inquiry."

But a Dart spokesman insisted it was "complete nonsense" to suggest that Lappin's departure indicated any loss of resolve to exploit coalbed methane in Scotland. With the "operational phase stalled" and the project at the appeal stage, "his job was done", the spokesman added.