Share or loan interest (including dividends) is normally paid or credited to the shareholders in a credit union without deduction of tax (ICTA88/486 (2)). It is chargeable on the shareholders under Case III of Schedule D in accordance with ICTA88/S486 (3).
Credit unions are required to make returns under ICTA88/S486 (6) in respect of share interest paid. There is further guidance on this at AP3783 and AP3784.