Staff who look after racehorses are paid as little as pounds 1.98 an hour, which over a normal working year would translate into a wage of less than pounds 4,000.
Joint bottom of the low-pay league was Axa Provincial Insurance, based in Kendal, Cumbria, the report - "Pay Systems and Pay Structures and the Relationship to Low Pay" compiled by Incomes Data Services - found. Axa Provincial claimed, however, that no one was actually paid less than pounds 3.17 an hour.
Responding to the findings, a spokesman for the National Trainers' Federation for horseracing said that the pounds 1.98 an hour rate applied to school leavers and was a "safety net". Many employees were paid more.
Junior hairdressers, who received as little as pounds 2.18 an hour, are also among the poorest workers, according to the study for the commission which will advise ministers on the level at which the national minimum wage should be set.
The Government is expected to set a minimum of around pounds 3.50 an hour at current prices for workers over the age of 24.