Our members are more than a bit frustrated at the differences in pay

Sheila Pickman, PCS union

Sheila Pickman, chief negotiator for the PCS, said differences were between �1,500 to �2,500 a year, but up to �3,500 in some cases.

She told BBC News Online: "Staff from the former Ministry of Agriculture are working alongside colleagues who are earning substantially more.

"Our members are more than a bit frustrated at the differences in pay.

"This action is not intended to target foot-and-mouth areas, our grievance is with what used to be Maff."

More than 600 workers failed to turn up at Defra centres at Eden House, Carlisle, and Crosby Road, Northallerton, as well as at Defra premises in Reading, Berkshire.

More strikes

Mrs Pickman said: "We have a large number of staff here who are on the national minimum wage and who have to supplement their salaries with second jobs or with benefits.

"People have a vision that civil servants are very well paid and they are not."

She said other Defra centres would be affected by action in the week beginning 17 September, and the union position would be reviewed at the end of a four-week period.

As well as the pay differentials the PCS put forward a request for a 10% pay increase in January, but was offered 3.5% in June.

Across the UK there are about 3,000 union members who are former Maff employees.

Foot-and-mouth

Up to 1,000 of them work in Cumbria, where farmers have been severely affected by the foot-and-mouth crisis.

As well as the 350 staff at Carlisle, 650 more are employed on sites at Workington, Penrith and Kendal.

They are responsible for ensuring subsidy payments to farmers.

Mrs Pickman said staff would do their utmost to ensure these were not affected.

A spokesperson for Defra said management and unions were in discussion about the pay differences.