Apple appears to be ploughing ahead with plans to build a driverless car.

The Silicon Valley titan has poached Elon Musk's former chief engineer to work on its top-secret automotive project. Doug Field's appointment has reignited speculation about the iPhone maker's car programme after reports it had been dropped.

The 52-year-old has worked at Musk's Tesla for the past five years as vice-president of engineering, and is credited with helping to make the vehicles easier to build.

Rumours he had left swirled in May as troubled efforts to ramp up production of its Model 3 sedan came to a head. His exit was confirmed last month, despite Tesla initially claiming he was simply taking leave.

Field, previously a vice-president of hardware, will now join Bob Mansfield, a top engineer brought out of retirement in 2016 to head secretive research and development programmes.

These reportedly include the Cupertino-based firm's automotive efforts, Project Titan.

It was claimed last year that Apple had scaled back the project to focus on software for driverless cars. But a recent court case revealed its efforts were far greater than acknowledged.

As many as 5,000 people are potentially involved, with court documents revealing Apple was developing key components such as power and battery systems, as well as suspension mounts.

At Tesla, when Musk took charge of production from Field, he tweeted: 'Doug, who I regard as one of the world's most talented engineering execs, is focused on vehicle engineering. Better to divide and conquer.'

Musk added: 'He has not left Tesla.'

But in July, however, it was announced Field had left.

John Gruber, an Apple expert who writes the Daring Fireball blog, said Field was 'a seemingly perfect fit' for Apple. He said: 'It's an interesting hire, primarily because it suggests that Apple still has an interest in making actual vehicles.'

He said rumours that efforts were being scaled back did not make sense, adding: 'Apple's modus operandi has always been to make the whole widget. It makes products, not components. Field returning suggests that under Mansfield's leadership, the Titan project has regained its footing.'

Recently, some analysts have suggested Apple should buy a stake in Tesla using its vast cash pile. Despite suggestions the tech giant, which recently hit a $1trillion valuation, could consider acquisitions, chief executive Tim Cook has instead ploughed money into a huge share buyback.

But Ross Gerber, boss of US wealth manager Gerber Kawasaki, said: 'On the car side, how Apple hasn't taken a stake in Tesla will go back in history as one of the biggest mistakes in Tim Cook's career.

'This is an opportunity for Apple to buy 10 per cent or 20 per cent of Tesla.

'We really think Apple has to start thinking about this. They are hitting it out of the park completely with everything that they are doing from the past - but it's the future that we're focusing on.'

Tesla declined to comment.