The announcement from Royal Bank of Scotland that it is making a one-off payment of £4.2 billion payment to its pension fund, instead of making phased payments, illustrates how pension liabilities are increasingly crucial to UK banks' overall financial health.

The move, announced on January 27, also throws a spotlight onto the vexed question of how the UK banks and their regulators plan to split up their giant retirement schemes when their retail arms are ringfenced in 2019, separating their retail-banking operations from supposedly higher-risk investment banks.