Born in April 1924, Jeffreys started her research career in 1949.

Later Jocelyn moved on to work for BMRB before joining RBL/Research International. For many years in the 1970s she worked in the Overseas Research group in RBL.

One of her claims to fame was that during her time at BMRB she helped train a certain George Vasiliou, who later became president not only of his own very successful research company but of his country, the Republic of Cyprus. The members of the Overseas Group at RBL were reminded of this each year when a box of delicious oranges and lemons would arrive from Cyprus.

Following RBL, Jeffreys moved to Taylor Nelson and later moved on to the client side and ended her long, eventful career in market research with the drinks company Allied Domecq.

Her funeral was held at East Finchley Crematorium on 22 July.