There's also anger over the size of Diamond's £17m 2011 pay packet.
The size of Diamond's tax bill and his pay packet is highly disturbing when you consider the share performance of Barclays. Currently (at time of writing, 14.00, 11 April) Barclays shares are worth 215p. Roll back a year ago and they were worth around 315p. A 32% slump.
It gets a great deal worse if you extend the timeline. Stretch back to 2007 and Barclays shares were worth more than 720p. A 70% drop. Admittedly Diamond was not at the helm of the company in 2007, but he is certainly making a lot of money from a bank that has seen shareholders badly damaged in recent years.
In the ABI's own 'Principles of Remuneration' guidance it makes very clear that making payments to compensate for any changes in an exec's personal tax status is a serious breach against boardroom governance.
Words vs ActionWhether the ABI will flash a 'red top' - a higher grade warning than 'amber' - remains to be seen. The other issue the ABI is clearly concerned about is the size of Diamond's pay-out. How can anyone in corporate life expect to be paid a bonus of roughly 200% of of their annual salary in a year where the share price has crumbled?
The ABI aren't officially making any comment about the situation, other than to confirm the Amber Top warning. It's for shareholders themselves, big and small, to express a view now. These shareholders, indirectly, represent most people who have a pension. Which is a lot of us.
"The only way that banks will win back the public's trust is to become better citizens," wrote a leading banking boss last year in the Guardian. "That starts with how we behave, and in demonstrating we act with trust and integrity."
The author? One B. Diamond. Yet just three months later Barclays was ordered by the Treasury to repay £500m in tax avoidance measures, despite previously committing itself to a code not to engage in tax avoidance.