Drivers are being urged to remove four things from their cars before tomorrow, the hottest day of the week. On June 19, temperatures are set to soar to 32C in the capital according to the Met Office, meaning cars will become unbearably hot.

Even on a milder day of about 21C, the temperature inside cars can quickly soar to over 46C, according to a study in the journal Pediatrics. So in temperatures exceeding 30C, some everyday items left inside can be rendered useless, or at worst, may become harmful for use.

Plastic water bottles

One of the worst offenders is plastic water bottles, as the scorching heat can potentially cause chemicals to leak from the plastic into the water, making it unsafe to drink.

In the worst-case scenario, if a water bottle is left in direct sunlight, it could even act like a lens, focusing sunlight onto car interiors like seats or carpets, which could become a fire risk.

Suncream

Another essential item in the heat but useless if left in the car is sun cream. In high temperatures, the plastic bottle can become brittle, and pressure can build up inside, which could cause the bottle to explode and make a mess inside the car.

According to some dermatologists, sun cream should be stored at room temperature below 25 °C and away from direct sunlight. Any higher than that can drastically reduce its efficacy.

Medicine

Common medicines, including paracetamol and other painkillers, can also lose their efficacy in extreme heat. The maximum storage temperature for medicines will usually be stated in the instruction leaflet.

Electricals

Electrical items with batteries inside should not be exposed to extreme heat either, and in most cases, they should be kept under 40C.

This includes items like smartphones, cameras and laptops, which have large batteries inside. While exposure to these temperatures can make devices less effective, they may catch fire in particularly hot weather.