If a garage tank has not been properly cleaned, bacteria can form jellyfish-like blobs in the mixed fuels, which can eventually clog car filters, increase engine wear and destroy seals and pipes.

Since the government started requiring fuel sold in the UK to contain at least 2.5 per cent biofuel, garages have reported an increase in complaints regarding the above.

Businesses are now being warned that they must flush out their tanks regularly to avoid these complications.

Motorists have been warned to avoid fuel sold on the black market or at disreputable garages.

The problem may be worse in cars with older systems, as they are not designed to be compatible with the organic content of biofuels.