5 Invalid notices
1 Where—
(a) a demand notice is invalid because it does not comply with regulation 3(1),
(b) the failure so to comply was due to a mistake, and
(c) the amounts required to be paid under the notice were demanded in accordance with Part V of the Administration Regulations,
the requirement to pay those amounts shall apply as if the notice were valid.
2 Where a requirement to pay an amount under an invalid notice subsists by virtue of paragraph (1), the billing authority shall as soon as practicable after the mistake is discovered issue to the liable person concerned a statement of the matters which were not contained in the notice and which should have been so contained.