Marks & Spencer has insisted that its shelves will be well-stocked over a barbecue weekend with stock availability ‘looking better every day’ after it suffered a devastating cyber attack.

The company has been reeling ever since it was hacked over Easter – leaving grocery shelves empty and forcing it to stop taking clothes orders online. But M&S said stock levels are back to normal.

The update came as crooks thought to be behind attacks on M&S and the Co-op said the latter escaped the worst of the hack by quickly taking computers offline.

By contrast, M&S has been struggling for weeks and its shares have fallen more than 13 per cent since Easter, wiping more than £1billion off its value.

M&S said yesterday: ‘In chilled areas of stores, customers can buy what they need, while in our grocery departments stock is arriving in a more normal delivery pattern. Availability is therefore looking better every day.

‘We are particularly well stocked with the warm weather ranges, like BBQ, fresh bakery, fruit and veg, deli and picky bits.’ 

But bosses would not confirm when its website and app – offline since April 25 – would return. M&S is thought to be losing £43million a week, according to Bank of America analysis.

Other retailers, including Harrods and the Co-op, have also been targeted by the same gang, DragonForce.

Last night luxury brand Dior said it was contacting some customers over a cyber attack.

It was not clear if this was the work of the gang. The Co-op blitz was thwarted when it took computer services offline, hackers told the BBC. 

‘They yanked their own plug – tanking sales, burning logistics and torching shareholder value,’ they said. The Co-op said its stock systems were recovering.

Experts say the scale of the M&S attack means a ‘large chunk’ of the British population has been put on alert that their data may have fallen into the hands of criminals.

Although this did not include any card or payment details or account passwords, the retailer has told customers to be vigilant, saying they may ‘receive emails, calls or texts claiming to be from M&S, when they are not’.

The US cryptocurrency exchange Coinbase said hackers have stolen customer data and are demanding a ransom of £15million.