People are getting dementia earlier, with those in their late 40s now regularly diagnosed with the disease.

Two decades ago, early-onset dementia was usually diagnosed in patients in their late 60s – but it is now often striking those who are even younger, a study found.

Researchers warned of a ‘silent epidemic’ and believe environmental factors are playing a key role in its increasingly early development.

While the study found no single factor was responsible for the rise, pollution from aeroplanes and cars is believed to play a ‘major part’.

Colin Pritchard, a researcher from Bournemouth University, told The Times: ‘The rate of increase in such a short time suggests a silent or even a “hidden” epidemic, in which environmental factors must play a major part, not just ageing.’