Uber's European expansion plans have suffered a setback after one of Europe's leading judges ruled that it should be treated as a transportation firm - not a tech firm as the company has argued.

Advocate General Szpunar is a key advisor to the European Court of Justice - but his opinion is non-binding.

If the company is judged to be a transportation firm this will raise the level of regulation which it will face in European markets.

The firm does not own any cars and its drivers are technically self-employed. It argues that it is a technology firm providing a platform - not a transport business.

"Taking account of the fact that the supply of transport constitutes, from an economic perspective, the main component, whilst the service of connecting passengers and drivers with one another by means of the smartphone application is a secondary component, the Advocate General proposes that the Court’s answer should be that the service offered by the Uber platform must be classified as a ‘service in the field of transport’," the ruling stated.

The ECJ is not required to follow this guidance - but its rulings generally do.

Here's the company's response:

"We have seen today's statement and await the final ruling later this year. Being considered a transportation company would not change the way we are regulated in most EU countries as that is already the situation today.

"It will, however, undermine the much-needed reform of outdated laws which prevent millions of Europeans from accessing a reliable ride at the tap of a button."