Jaguar bosses have been warned they must keep their high levels of quality - or face closing one of their UK plants.

Industry experts at Warwick Manufacturing Group - a think-tank, based at Warwick University which advises Jaguar and Land Rover - stressed it is essential the luxury-car maker retains its market share in the US.

It says Jaguar needs to be positive in its approach in the long term, or be prepared for further difficulties.

Jaguar, which has a plant in Browns Lane, Allesley, Coventry, is planning to cut production after a drop in demand in the US market which bosses blame on the weak dollar.

But Nick Matthews, a principal fellow at the think-tank, said the exchange rate was only one issue facing the car giant at the moment.

He said: "I suspect the reason why it is happening now is the dollar but the danger that they have got to be aware of is that it does not become an excuse.

"The US market is absolutely vital to Jaguar.

"They are selling more cars but they are not selling as many as the market is growing - they are losing market share. The market is getting bigger and bigger but Jaguar is not getting as big a share as they should be getting. There's argument that the costs of producing relatively small numbers in three different places are a cost burden.

"This is the argument that has been going on for months about whether Browns Lane is needed.

"Obviously if they do not increase the volume it will become more obvious that they will have to make cost-cutting measures."

The car manufacturer has 2,500 staff at its Browns Lane plant, where the XJ and XK models are made. A further 2,300 people work on the S-Type at Castle Bromwich, while 2,500 workers produce the X-Type model at Halewood, on Merseyside.

Mr Matthews added: "One of the problems they are up against in the US market is manufacturers like Toyota and BMW have plants in the States.

"BMW have a plant in Kentucky so they are not affected by currency fluctuations in the same way.

"Jaguar's problem is the size of the market in the US. In Britain, it is in a narrow market - the market for upmarket cars is small but in America it is relatively big and quite large so there's more competition.

"The longer term challenge is to maintain the quality of the product so that people want to buy it whatever the price is."