Spanish taxi warning issued by UK Foreign Office and it could cost you £500

UK travellers heading to Spain this summer are being warned about a little known rule that could end up with a very costly fine.

And it's no joke, with official advice coming your way via the UK Foreign Office.

Brits head to Spain more than anywhere else, with it the most visited country year on year as millions fly to the country to enjoy its gorgeous beaches and historic towns and cities.

Because so many of us go there, there's plenty of advice on what you need to follow in order to avoid a fine or two. This includes taking a key document with you if you're staying with friends or family that'll stop you from being turned away and sent home.

There's also toughening rules in regards to overstaying your legal welcome; rules that if broken, could see you banned from most of Europe for three years.

Millions of us rely on taxis during our holidays in Spain (Getty Stock Images)

Other rules are a little more obtuse and concern breaking the law while listening to music or heading to Benidorm's famous beach.

And yet here we are, with another rule that's not known by many tourists.

If broken, you're looking at a fine of €600, which equates to roughly £510. Not what anyone wants on their holidays.

The rule concerns getting a taxi and making sure the vehicle you're in is legit, with a proper license to carry you.

Advice from the UK Foreign Office has stressed the important of using recognised and licensed taxis or transport services.

Make sure everything is above board (Getty Stock Images)

The guidance on its website states: "Only use official registered or licensed taxis, or reputable transport companies you recognise.

"Licensing regulations differ across Spain and in certain cities pre-booking is required."

The warning continues: "Passengers caught using unlicensed taxi services are liable for fines of up to 600 Euros.

"Make sure you book your taxi or airport transfer through a licensed firm."

It comes as a general warning has been issued by the Spanish government over extreme temperatures.

Legit taxis will avoid the risk of a fine (Getty Stock Images)

Spain has recently launched a new temperature checking system that the national government is urging natives and tourists alike to use in a bid to save lives. It follows the death of 22,000 people from heat-related illness in recent years.

The Spanish Ministry for Health said: "Exposure to high ambient temperatures can cause an insufficient response of the human thermoregulatory system.

"Excessive heat can alter our vital functions if the human body is not able to compensate for variations in body temperature."