Gas prices in the Mediterranean are rising by more than 50% in some regions, according to some supermarkets.
The latest rises have been driven by soaring petrol prices and the threat of rising electricity tariffs.
Some supermarkets, including a supermarket in the seaside town of Capetown, said their staffs had to take longer to clear their shelves because of the heat.
Many customers were also unable to get home because of high heating bills, causing delays to many customers, including those who live far away from the coast.
The rise is the biggest since March 2016.
The National Grid said it had seen an increase in demand for gas due to the heatwave.
A spokesman said the rise was because of higher fuel costs, which have driven up petrol prices.
Gasoline prices rose by around 50% this month.
Grocery chains including Aldi and Tesco have been hit by a spate of fires in recent months.