Almost half of the rise has been among people aged 50 or over, with the fastest rate of increase occurring among those 65 or over, according to independent research organisation The Institute for Employment Studies (IES).
The IES has said that there are now almost a million people aged 65 or over in jobs, double the number 10 years ago and up 13% over the past year.
The IES claims that even though these older workers comprise only 3% of the working population, they account for 20% of the recent growth in employment.
It also states that there is no evidence to suggest older workers are gaining employment at the expense of the younger generation. Over 65% of 65 year olds work part-time, compared with 39% of 16-24 years and 30% of older workers work in managerial and professional jobs compared with only 9% of younger workers.
Jill Hillage, director of research at the IES, said: "There are a number of reasons why older workers are staying on in work. In some cases employers want to retain their skills and experience and encourage them to stay on, albeit on a part-time basis. Older employees have been working for their employer for at least 10 years and often in smaller workplaces.
"Some older people have to stay in work as their pensions are inadequate and it is interesting to note that employment of older workers is highest in London and the south east, where living costs are highest."
Hillage added: "There is also a growing number of self-employed who still want to retain their work connections and interests."
