Here.
http://stakeholders.ofcom.org.uk/binaries/telecoms/ga/cvogc18032010.pdf
GC22, page 68,
1.5 The Communications Provider shall communicate the MAC to the End-User in writing by letter and/or by e-mail within five working days of receipt of the End-User’s request save for A1.6.
A1.6 Where the Communications Provider has issued the MAC to the End-User over the telephone (including details about the MAC validity period and expiry date and the Broadband Service to which the MAC relates), the Communications Provider is not required to communicate the MAC to the End-User in writing.
A1.7 The written response (e-mail or letter) to the End-User containing the MAC shall clearly indicate:
(a) the MAC (or MACs);
(b) the MAC validity period and expiry date; and
(c) the Broadband Service(s) to which the MAC(s) applies.