The £12 billion annuity book sale will see around 400,000 policyholders transfer to Rothesay, which is backed by Singapore sovereign wealth fund GIC and Blackstone.
The jumbo sale leaves around £20 billion of annuities on the books but M&G said it had no plans to sell more. By splitting off the UK, Prudential Plc also escapes onerous Solvency II rules on capital.
Panmure Gordon said the separation will take until 2020 and the demerger would allow its Asian operations to have a higher value.
Jefferies said the demerger would cut in half a “conglomerate discount” applied to Pru’s shares because of the unwieldy structure.