Around 84 warehouse staff staged a 48-hour walkout from at 6am yesterday, following a one-day strike last week. Unite has warned that a three-day strike will follow next week if negotiations are not forthcoming.

Unite national officer Steve Sibbald said: "There has been no movement from the company yet. The strikes will keep getting ramped up until they agree to sit down with us."

Warehouse staff at the company are pushing for a 4.2% pay increase, after agreeing to forego a pay rise last year, while the rest of the business received a 2% increase.

All employees were originally offered a 2% increase this year; however the warehouse staff rejected this deal and argued that they should be awarded a 4.2% to bring them level with their colleagues in the rest of the company. The company came back with a 2.5% final offer, which was also rejected.

A statement from OUP said: "We believe we have made a fair and reasonable final offer. OUP’s pay and benefits for its warehouse employees are very attractive compared to rates for similar roles in the area.

"We have been keen to maintain constructive dialogue with Unite representatives throughout the negotiation, and are disappointed at the outcome of the ballot.

"We have plans in place to minimise any impact on customers, and do not anticipate service disruption.

"OUP has also recently made a significant commitment to both our employees and to the North Northamptonshire area through investing in new facilities at ProLogis Park."

The company added that the site remained open and service levels were unaffected.