671. Assessments to corporation tax.

If an officer of Revenue and Customs discovers1 as regards an accounting period2 of a company that:


    (1)     an amount which ought to have been assessed to tax has not been assessed;


    (2)     an assessment to tax is or has become insufficient; or


    (3)     relief has been given which has become excessive,

the officer may make an assessment (a 'discovery assessment') in the amount or further amount which ought in his opinion to be charged in order to make good to the Crown the loss of tax3. If an officer of Revenue and Customs discovers that a company tax return4 delivered by a comp