Staff at Tesco will be told next week that pay rates for working Sundays and Bank Holidays, late nights and overtime hours are set to be slashed as the supermarket giant seeks to cut costs, This is Money has learned from a source.

It is believed employees at the retailer used to receiving double time for Sundays and Bank Holidays will be told on Tuesday that they will get just time and a half from July - a pay cut of 25 per cent.

Higher pay rates for overtime will also be revoked, with extra hours paid at the standard rate, according a whistleblower who wishes to remain anonymous.

And a premium for working the hours 10pm-midnight will be scrapped as part of the pay review. This is Money understands it was a deal agreed behind closed doors with the Union of Shop, Distributive and Allied Workers.

Pushing for less: Tesco staff will see pay rates for certain anti-social hours fall from July.

A Tesco spokesperson said in response to the claims, 'We have reached a positive agreement on a two-year pay and benefits package for store colleagues, which is one of the most competitive packages in the supermarket industry and is good news for the large majority of colleagues.

'We will announce details of the deal once we have spoken to colleagues about the changes. Any colleagues out of pocket from the premium changes will be given advance notice and earnings will be protected for up to two years.'

On an online forum, 'Very Little Helps' – one user said: 'Loyalty and commitment means nothing to Tesco any more, we are all just a number sold down the river.'

The grim news for employees comes after Tesco announced this week that it would cease 24-hour trading at 76 of the 400 stores nationwide that currently open all hours.

That in itself will limit earning opportunities for staff used to having the option of working a certain number of hours.

According to Tesco the reduction in opening hours would free up staff to replenish more products on the shelves overnight, resulting in more item availability and stores looking better. It added there will be a 'minimal' impact on jobs as a result of its decision.

The moves are the latest planks in chief executive Dave Lewis's drive to cut costs at the retail behemoth and turn around stagnant sales.

Tesco has been under severe pressure over the last few years, suffering unexpected financial reversals, while having accounting irregularities exposed that have led to litigation in the US.

Now UK investors are set to launch a huge damages claim, saying they lost tens of millions because of the accounting scandal at the supermarket.

Struggle to sell: Tesco's share price has suffered more than that of rival retailers over the last few years - but it has had more on its plate than just harsher competition.

Group litigation fund Bentham Europe has gathered institutional investors who believe they lost out when the retailer admitted overstating its profits by £250m.

Shares in the company plunged by more than a fifth in September 2014 when Tesco issued its third profit warning in weeks, saying it had uncovered a 'serious issue' within its accounts.

The retailer has also been hit by shifts in shopping habits and the loss of customers to discounters Aldi and Lidl. However, the supermarket recently reported that Christmas sales rose 1.3 per cent, well ahead of what industry experts had been predicting.

A testing week for the supermarket giant also saw an investigation into Tesco's treatment of suppliers report its findings.

'Extensive evidence' revealed the group 'intentionally delayed' payments to suppliers in order to make its own financial position look better than it was, Groceries Code Adjudicator Christine Tacon's inquiry revealed.

Tesco escaped a financial penalty because this power was only given to the Adjudicator after she launched her investigation.

In the 84-page report, Ms Tacon said: 'The length of delays, their widespread nature and the range of Tesco's unreasonable practices and behaviours towards suppliers concerned me.

'I was also troubled to see Tesco at times prioritising its own finances over treating suppliers fairly.'