The owner of Phase Eight, Hobbs and Whistles has said its websites and IT systems have been hit by a cyber-attack that may have compromised customers’ personal data.

The South-African listed TFG London said it identified the “cybersecurity incident” at the three UK-based retail chains on Sunday. Its two other UK brands, Inside Story and White Stuff, are not affected.

TFG said its stores had stayed open and trading but some of its IT systems “remain unavailable” and it had paused all online orders as a “precautionary measure”.

An “investigation is ongoing, including establishing whether any personal or other sensitive information has been compromised,” the company said.

If the investigation establishes that any personal information has been accessed by hackers, TFG said it would “notify affected individuals or organisations”.

“Some of our brand’s website capabilities may not be available as the investigation continues. We apologise for any disruption and will provide additional updates to our customers as appropriate,” the company added.

In an email to Whistles customers, the company said any orders placed on or after 11 October may be delayed. Orders placed before that date are being processed normally. Returns can only be made via stores at present and Whistles told customers it was “working on a solution for postal returns”.

TFG has engaged external cybersecurity specialists to contain the incident, which has been reported to the relevant UK authorities.

The group’s operations in Africa or Australia run on separate systems and are not affected.

The attack on the three UK fashion brands comes less than a week after a cyber-attack affected the online fashion seller Asos, in which the names, addresses and recent search data of millions of customers was accessed.

H&M said on Monday that it was also investigating claims that its systems had been attacked. However, the fast fashion retailer said: “We have not found any indications that our data environment has been compromised.”

On Monday, it emerged that hackers had forced the temperature of many French supermarket fridges up to 50C overnight, in an “unprecedented” cyber-attack affecting several hundred stores.

Several other British retailers, including Marks & Spencer, the Co-op and Harrods, were hit by damaging cyber incidents last year. M&S and the Co-op faced stock shortages and the former was forced to shut down its website for several weeks while it ensured its systems were clean.

Marijus Briedis, the chief technology officer at the digital security firm NordVPN, said: “Coming so soon after the Asos incident, this latest attack on TFG London is another reminder that the retail sector is firmly in hackers’ sights. These attacks are becoming a recurring nightmare for businesses, and there’s every reason to believe we’ll see more of them.

“Retailers are particularly attractive targets because they hold valuable customer information and rely on a sprawling network of payment systems, suppliers and third-party technology providers. Every connection is a potential weak point, and attackers are increasingly adept at exploiting stolen credentials, human error and gaps in security.”