— the weird and wonderful world of car extras

Naturally it should only be used when the car is stationary, as gadget tester Thomas Schuster from the Kues type approval organisation points out.

In theory any add-on which is not attached to something inside the car can be hazardous, said Arnulf Thiemel, a technology expert who works for the ADAC car club.

Even novelty nodding dogs or umbrellas on the rear parcel shelf can fly around the cockpit and injure an occupant if a driver needs to brake hard or take avoiding action.

Accessories offered by the car companies themselves are generally the better buy, since they have been properly tried and tested. The quality is reflected in the higher price.

Some of the most exclusive car accessories on the market come from British luxury automakers. They include motorized lunch tables.

The opulent Bentley Bentayga SUV offers the ideal extra for a tailgate lunch — a sumptuous picnic hamper. It fits snugly into the boot of the new off-roader and costs just 24,990 euros.

The set contains fine Linley china crockery, silver cutlery and crystal glass. It includes an illuminated cooling compartment to ensure that drinks are served chilled. Dry foods and a cashmere rug ensure a cosy al fresco lunch in the countryside. The Rolls-Royce version is even more expensive. Volkswagen will sell owners a more mundane insulated storage box for a fraction of the price, while for coffee fans there is a compact, portable coffee maker. It uses pads to brew either a long coffee, a cappuccino or a macchiato with no need to get out of the car.

For drivers who do not want an air refresher dangling from the rear-view mirror on a string, there are fragrance dispensers which pump perfume into the cockpit. They too plug into the lighter socket.

The rear massage seats featured in the luxurious Mercedes-Benz S-Class limousine can be bought aftermarket. Aftermarket models also use electric motors to operate panels which soothe away back pains and create that spa feeling in the back of the car.

In some countries strict laws govern what extras may be installed in cars.

In any case it is worth ensuring that picnic trays and accessories attached to seats do not prevent side airbags from inflating properly, said the German expert.

Plastic smartphone holders which can be clamped to the steering wheel are dangerous. If an airbag in the steering wheel inflates in an emergency, the telephone holder gets pressed into the driver’s face.