451. Availability of small companies exemption in case of group company

(1) A company is not entitled to the exemption conferred by section 449 (small companies) in respect of a financial year during any part of which it was a group company unless—
(a) the group—
(i) qualifies as a small group in relation to that financial year, and
(ii) was not at any time in that year an ineligible group, or
(b) subsection (2) applies.
(2) A company is not excluded by subsection (1) if, throughout the whole of the period or periods during the financial year when it was a group company, it was both a subsidiary undertaking and dormant.
(3) In this section—
(a) "group company" means a company that is a parent company or a subsidiary undertaking, and
(b) "the group", in relation to a group company, means that company together with all its associated undertakings.
For this purpose undertakings are associated if one is a subsidiary undertaking of the other or both are subsidiary undertakings of a third undertaking.
(4) For the purposes of this section—
(a) whether a group qualifies as small shall be determined in accordance with section 370 (companies qualifying as small: parent companies), and
(b) "ineligible group" has the meaning given by section 371 (2) and Error! Reference source not found. (companies excluded from the small companies regime)
(5) The provisions mentioned in subsection (4) apply for the purposes of this section as if all the bodies corporate in the group were companies.