Workers will be given rights to claim sick pay from their first day on the job under new laws.

The Government is expected to give more than seven million people the entitlement under changes to be unveiled on Thursday.

At present, most people are not allowed to claim sick pay until the fourth day of their illness.

Labour will announce what it calls a ‘once-in-a-generation’ overhaul of workers’ rights in the Employment Rights Bill.

Probation periods – which can currently last as long as two years – are also expected to be shortened to six months and staff will get protection against unfair dismissal from their first day at work.

Women are set to be entitled to apply for maternity pay from their first day rather than waiting six months. Ministers have also vowed to strengthen protection for new mothers against unfair dismissal.

However, small-business hopes for a government fund to compensate them for the cost of more sick pay are likely to be dashed. But ministers have offered some concessions to businesses, including abandoning a statutory ‘right to switch off’.

The plans could spark a backlash from businesses, which are concerned about the burden and cost of the new rights, and unions which think they do not go far enough.

Tory MP Gareth Davies said: ‘Only Labour could come up with an unfunded tax rise. It won’t just cost the Exchequer, it will hit growth and investment too.’

Some details of the reforms will be decided by ministers under delegated powers after Labour pledged to deliver the new laws within 100 days of taking office.

A government source said: ‘Our plan to make work pay has always been about delivering economic growth by increasing security for working people, improving productivity and levelling the playing field for businesses. Ensuring people have sick pay when they need it is crucial to that mission.’