The prospect of hundreds of new jobs being created at Longbridge has been held out by MG's owner under plans to dramatically increase car production at the plant.

It emerged with the announcement from Nanjing Automotive (NAC) that it is developing new models for the European market.

The firm’s official spokeswoman Eleanor de la Haye said at least 50,000 vehicles a year could be rolling off the production lines within the next few years.

Professor David Bailey, of Birmingham Business School, said the volumes were realistic but employment levels would have to double or even treble.

However, there was still a healthy amount of scepticism surrounding the new models and one industry insider said: "Nanjing has made promises like this before and not delivered on them so people are adopting an attitude that they will believe it when they see it."

The latest figure is way above the 5,000 TF sports cars which were originally planned to be produced and would require a significant increase in manpower.

About 140 people are currently employed at the plant but this would have to increase significantly if the 50,000 target was to be achieved.

Prof Bailey said: "The figure of 50,000 cars sounds about right to me. There is certainly capacity at the plant to do that but it would require several hundred new jobs.

"50,000 vehicles isn’t a significantly high amount, in fact it’s quite small for an assembly plant – 250,000-300,000 vehicles is around the figure for a full assembly plant."

At its peak, Longbridge was producing 345,000 cars annually. The firm collapsed in 2005 throwing 6,000 people out of work.

The CBI in the West Midlands said on Thursday it was dubious about predicted production levels because of the small number of people employed at the plant.

But Prof Bailey said: "The TF operation is relatively small and will have a minimal impact but this could change significantly when the new models are introduced.

"What has to be borne in mind are costs and so the question has to be, how much manufacturing will there be or will these cars just be bolt-togethers."

NAC, now merged with larger Chinese company Shanghai Automotive (SAIC), announced on Thursday that production of the MG TF LE500 would restart in August with the first cars arriving in dealer showrooms a month later.

But the firm said its designers were also working on new models and it is thought that at least four could be in the pipeline – an updated TF roadster and coupe, a large car, possibly an updated Rover 75, and two mid-range cars that share the same platform as the Roewe 550, which was unveiled at the Beijing motor show last month.

Initially TF bodies will be shipped to Longbridge from China and then assembled but long term it is thought the next generation of vehicles will be fully manufactured in the UK.

The announcement brought to an end to months of uncertainty regarding the future of the car plant.

There were fears at one stage that it had no future because of increasing delays to the TF project, caused firstly by poor quality Chinese components and then from NAC’s merger with SAIC.

Now the merger is complete, SAIC appears far more serious about producing cars at the plant than NAC ever did.

Professor Bailey added: "I don’t think Nanjing would ever have been able to pull off this kind of thing but SAIC is far more committed and I think the appointment shows its intent.

"It also shows that SAIC is exerting control over the situation and is making a firm commitment to the site, which again is a good thing."

St Modwen, the main developer behind the £750 million Longbridge Area Action Plan, last night welcomed the commitment from the Chinese company.

Mike Murray, senior development manager for St Modwen, said: "We are fully supportive of NAC looking to commence car production at Longbridge."

Part of SAIC’s commitment has seen it integrate its Leamington research and development centre with the factory at Longbridge.

It is thought the company sees the plant as a hub from which to enter the European market, although what the cars will be marketed as remains to be seen.

NAC cannot market them as Rover as the rights to that name lie with Tata following its acquisition of Jaguar Land Rover.

Ms de la Haye has said that neither would they be branded Roewe, as they are in China. This leaves MG as the most likely option.