Under FA89/S102 a group company may surrender a refund of tax to
another group company.
To calculate tax 'unpaid' for the purposes of a tax-related
penalty you treat the receiving company as having paid the amount
of the refund on the day the companies jointly gave notice of the
surrender. You do not use the 'relevant date', which is the date on
which the surrender is effective for interest purposes (FA89/S102
(5)).
Following reallocation of a repayment surrendered, COTAX
automatically calculates any tax- related penalty payable by the
receiving company taking account of this restriction.