A delay in delivery of Thomson Airways’ first Boeing 787 appears inevitable, with the Dreamliner grounded and investigators in the US and Japan unable to identify the cause of batteries overheating on two aircraft.

Thomson has said it had no details of any revised delivery dates, while Boeing is expected to issue fresh guidance today (Wednesday).

The carrier was due to receive its first Dreamliner in February and to start flying the aircraft on May 1.

Thomson clients expressed frustration at the lack of information, amid fears that they won’t fly on the 787 despite booking and paying a small premium.

David Stacey, who describes himself as “a long-time customer of Thomson” told Travel Weekly: “Thomson needs to offer customers the chance to switch or stick. It’s unfair.”

A spokesman for the airline said: “At the current time, Thomson Airways has not received any communication from Boeing regarding changes to delivery dates. Therefore we cannot comment on speculation of delays. Normal booking conditions apply for customers who wish to amend or cancel their holiday.”

Boeing said: “It is impossible to put a timetable on it. We have hundreds of experts working around the clock.”

A Boeing spokesman told Travel Weekly: “We are producing aircraft, but we’re not going to be delivering any 787s until the Federal Aviation Administration (FAA) approves measures to meet its air-worthiness directive.”

Investigations are under way in the US and Japan following a fire on a Japan Airlines 787 at Boston and an emergency landing in Japan by an ANA 787 when its main battery overheated. Both incidents involved new lithium-ion batteries used on the 787 as part of its innovative power system.

Officials in Japan ruled out a problem with the battery maker this week, while US regulators said they had made “no significant discoveries” since the aircraft was grounded in mid-January.

With attention shifting to the 787’s electrical system, analysts warned the grounding could be prolonged.