Confidence in job security for workers aged between 45 and 54 fell by 10% since October 2012 (when it was 79%) to just 69% in January 2013, the index showed. For workers aged 55 and over there was a 6% drop, to 76%, in confidence in their job security over the same period.
The index also found that older workers confidence in their job security fell when compared with findings for the same time last year.
Although the index shows a decrease in job security for older workers over the last quarter, there has been an increase in confidence in job security for younger workers. Those aged between 18 and 24 were the only age group to show increased confidence in their job security since October 2012, increasing by 4%, from 76% to 80%.
Conversely, the index found that confidence in job security among the 'sandwich generation', those aged between 35 and 44, has dropped to its lowest since the research began, falling to 70% in January 2013, from a high of 77% in October 2012.
It reveals this group are also the most likely to say that they think they will worry about how they will maintain their current standard of living in 2013 (60%), compared to a national average of 54% among all workers.
Those aged between 45 and 54 are the second most likely to worry about how they will maintain their standard of living in 2013, with over half, (54%) saying they'll definitely or probably worry in 2013.
Mark Holweger, director at Legal & General's insurance business said: "Concerns about younger people being able to find employment is regularly making the headlines, but for those who are already employed, it is the older workers, who are most concerned about their future job security.
"With an increasing number of older workers having to continue to work for longer than they had planned, it is understandable to see them becoming increasingly worried about their future job security."
Mark Holweger continued: "What is really worrying is the drop in confidence in job security for the 'sandwich generation' - those who potentially have both children and elderly parents who are dependent on their income.
"The fall to 70% is an all-time low since the Job Security Index was launched last year. They are the ones most likely to have to stretch their income to cover a range of essential outgoings for their wider family members.
"So with such a significant number of them worried that they may not have a job to provide a steady, secure income for their families in the future, a contingency plan to pay essential bills and keep the family afloat if they were to lose their job is crucial."
The Legal & General Job Security Index is based on research conducted for Legal & General by YouGov of 2686 UK representative employed adults, either employed full or part-time or self-employed, over the period 3rd - 6th January 2013.
