An interest-rate scandal is costing Bob Diamond more than a few carats.

The disgraced Barclays Capital CEO, who was forced to resign as head of the UK’s No. 2 bank last week, is forgoing some $31 million in deferred pay amid an interest-rate scandal that has ensnared Barclays top brass and UK regulators.

Barclays Chairman Marcus Agius told British UK lawmakers yesterday that Diamond’s pay would be restricted.

Barclays has agreed to pay approximately $450 million to UK and US regulators related to charges that the big bank’s traders falsified a key interest- rate benchmark known as the London interbank offered rate.

Agius’ meeting last night in London follows a pair of intense sessions lawmakers conducted with Diamond on July 4 and Bank of England Deputy Gov. Paul Tucker on July 9.

During Agius’ meeting, lawmakers threatened to bring Diamond back for more testimony after new documents contradicted Diamond’s earlier testimony.