The Agency does not approve alternative means of compliance. That responsibility rests with the competent authorities of the member states. The Agency will make a recommendation to the Commission following a request by a member state for approval of other means of complying with essential requirements than those prescribed by implementing rules but that's an exemption rather than an AltMoC.
AltMoCs developed or approved by UK CAA are published in CAP 1721. An index of AltMoCs notified to the Agency is published here (
link). None of these contains the text quoted in post 3 above.