NatWest Group has blocked messaging services WhatsApp, Facebook Messenger and Skype on company devices to prevent staff using them to communicate with each other.
The bank had previously asked its employees to stick to “approved channels” for conversations on professional topics.
But now it has gone further and made the platforms inaccessible on business phones and computers.
So-called off-channel communications are a persistent problem in both business and politics, with concerns that services such as WhatsApp are being used to reduce the scrutiny to which certain conversations may be subject.
Messages can be difficult to recover, or even disappear, while those sent through approved channels are fully recoverable, meaning they can be investigated if wrongdoing is suspected.
“Like many organizations, we only permit the use of approved channels to communicate on business matters, whether internally or externally,” NatWest said in a statement.
The change took effect earlier this month.
US banks have been fined more than $2.8bn (£2.18bn) in recent years over record-keeping rules – with employees unable to recover old messages from certain email services.
JPMorgan Chase, Wells Fargo, Bank of America and Citigroup are among those who will face sanctions.
It was reported in August that Britain's banking regulator, the Financial Conduct Authority (FCA), was considering investigating how bank employees use messaging services.
It follows a fine imposed by energy regulator Ofgem on Morgan Stanley for calls made to private phones via WhatsApp, in breach of record-keeping rules.
Outside of the banking sector, there have been problems with staff using apps in the public sector, with questions over how ministers have used WhatsApp for government business in recent years.
Britain's Covid inquiry found officials and ministers deleted WhatsApp messages exchanged during the pandemic.
This included Boris Johnson, then prime minister, and Penny Mordaunt, then a cabinet member, who told the inquiry that two years of messages with him had gone missing. Johnson told the inquest he had lost around 5,000 messages.
