Map shows areas of Sussex most affected by radioactive gas Radon

But high levels of this radioactive substance can increase the risk of lung cancer.

Radon is formed by radioactive decay from the small amounts of uranium that can be found naturally in all rocks and soils - so it is found everywhere.

The UK Health Security Agency (UKHSA), however, states that "every building contains radon but the levels are usually low.

"The chances of a higher level depend on the type of ground."

The radiation emitted from the elements can increase the risk of cancer and it appears that those living in rural areas are surrounded by more levels of this radioactive gas than more urban areas.

Over time, exposure to radon can cause lung cancer - and is responsible for 1,100 deaths each year in the UK.

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Much of Sussex is at higher risk compared to the rest of the UK - with homes along the coast typically at a maximum 30 per cent risk. 

Homes near Lewes and Westdean, near Seaford, are most at risk with a 30 per cent radon potential.

In Eastbourne, homes in the west end are more at risk than those in the east - with less than one per cent of homes at the action level in the east end of the town.

Map shows radon levels in Brighton and Sussex (Image: UKHSA)

Central Brighton sits at a three to five per cent radon potential while Hove is at a one to three per cent risk.

In less built-up areas like much of the South Downs, there is little to no risk with less than one per cent of homes near the level which requires action.

You can find out if your home is affected by using this interactive map.

The risk posed by radon can be lower in the countryside, including the South Downs (Image: UKHSA)

In advice to residents on its website, Brighton and Hove City Council said:  "The majority of Brighton is rated at one to three per cent risk of Radon, with some areas being higher. 

"This means that for every 100 houses in the area, you may expect one to three of them to have levels above the "action level" for radon of 200 Bq/m3. 

"Without testing, you could not state whether a property will contain Radon levels in excess of the 'action level'.

"Public Health England sells Home Measurement Packs. These tests take 3 months and require the house to be occupied at the time."

Russell Lawley, principal geologist at the British Geological Survey, previously said: "Radon occurs in all rocks and soils. Using a revised statistical approach to our mapping of geology across Great Britain has enabled us to model where this geo-hazard is more likely to be present in buildings."