There were 12.8 million working-age parents in spring 2004, which equates to 35% of the working age population.
The Acas helpline has received over 100,000 calls relating to holidays and Working Time issues in the past year. Questions include issues about annual leave being refused, current holiday entitlement and flexible working arrangements to cover the school holidays.
John Taylor, Acas chief executive, said: "Many businesses receive an increase in holiday requests over the summer and an employer often has to balance the needs of the business with keeping a healthy and motivated workforce. We always encourage employees and employers to plan ahead and be as flexible as possible."
Acas has issued practical guidance on holiday workplace rights. For further information visit the Acas website www.acas.org.uk/summer
