One of Marks & Spencer's largest suppliers has resorted to using pens and paper as orders, as retailers' cyberattacks continue.

Greencole's owner, who serves sandwiches, rolls and parcels, said it also added five-fifths of goods to ensure there is enough food for the bank holiday weekend.

M&S has been unable to provide online orders for clothing and household goods for over a week, and some stores have seen empty shelves as food delivery has also been destroyed.

Two M&S workers told the BBC they were worried about wages because they couldn’t get in and out of work and had no access to employee apps.

Greencore CEO Dalton Philips, who has glimpsed the situation behind M&S, said: "Without all the systems talking to each other, you can get back to what you were 25 years ago."

That means going back to "pen and paper," he said.

Greencore has also made more transformations at its dedicated M&S factory in Northampton, investing more vans on the way and providing more food to stores than during Christmas.

"They are our huge customers and we are working to help them overwhelm their products," Philips said.

“Sometimes, you do need to restore the manual system in any business…but look, it works well.

“We don’t have the complex predictions we’ve had before under the challenges of the system, so we’re just making sure they have everything they need and there’s more.”

George is not his real name, working at M&S ​​in Wales and said it was a "nightmare".

“We were told that we would be given a salary through a separate payment system. However, we have not been told whether the salary is correct.

“In addition, there are round-trip instructions that change every hour.

Jeannette Pellen, 76, of Doncaster, retired as an M&S customer assistant at the Scunthorpe store in late April, said they were unable to get in and out of work due to the attack.

“There is no way to receive advice through managers or outsourcing HR,” she told the BBC.

M&S reassures employees that they will pay for all contract time as usual.

As the former CEO of supermarket chain Morrisons, Mr. Philips is very familiar with the pressure on M&S bosses.

“They will actually be working 24/7. You have to work through it. They are really impressively calm and focused whenever I talk to the team this week.

“I think if you’re in retail, you know that people are usually the biggest games in their games and are driven during those huge stressful times.”

Greencore has also sent its own few employees to major M&S stores in London to provide additional support.

M&S has not released details on how its system has been affected, saying only that some people temporarily brought it offline to the limited availability in the store.

A food industry veteran who knows the business very well believes M&S will focus on making sure it still offers all the best-selling items.

“The problem is, if you have 7,000 products, then obviously that’s a lot of data to be reviewed.”

But he also pointed out that for large seasonal events, many will be purchased in advance and the company will have historical backups. Suppliers will also have some understanding of what sells well.

Ged Futter, a former buyer at ASDA, now running his own consulting supplier, said M&S is in a difficult position but thinks it will find a way in the retailer's side, as retailers are very good at finding solutions.

"They will use a fax machine if needed. The mindset of any silo is gone and everyone is very clear about how to fix it."

However, the longer this situation takes, the risk of damaging the M&S reputation and the increase in its customer loyalty.

The company has been praised for its communication with its customers, but remains silent about the nature of the attack and how it has evolved. This may be unsustainable.

Liam Byrne, chairman of the Commerce and Trade Commission, has written to M&S CEO Stuart Machin for assurance and said it is "a priority" to understand what happened.

One person, a former CEO of another company, had to deal with a data breach, told the BBC's PR consultant's advice was simple.

"Say nothing until you know everything. And then say everything. And then say nothing."

M&S has been contacted for comment.