Is Loan Write off Taxable?

Hi,

Mr A is sole director/Shareholder of Company

Mr B joins Company and is given 50% of the share capital and
becomes a director.

Mr B personally loans company £25,000

Mr B agrees to have £25,000 loan written down to £15,000 due to
Mr B  leaving company after disagreement with Mr A.

Accountants treat £10,000 write off as  income chargeable to corporation tax

Is this correct?

Thanks  in advance