The PLA, although a QUANGO, is permitted to ignore Freedom of Information requests. However they are subject to the very similar (and little known about) Environmental Information Requests. Thses are very similar but you have to link your question to environmental matters, which is not difficult given the PLA's role. The PLA tried to oppose this and OPLAC's research director John Hibbert won this case in front of the Information Commissioner about it. Contact email@example.com for more info.
Further relevant info:
c) A body/person that carries out functions of public administration
However, in the case of Port of London Authority v Information Commissioner (EA/2006/0061 and 0062) the Tribunal concluded that the Authority did exercise administrative functions. In coming to this conclusion it considered numerous factors:
The Authority has statutory duties. If the Authority did not fulfil those duties Government would need to task another organisation with them.
The Authority has to account to Parliament as well as to its shareholders.
The appointment of the Board is heavily influenced by the Secretary of State.
The Authority must report annually to Parliament on all its functions so there is nothing to suggest that some of them are regarded as private and the authority must give the Minister such information as he requires in relation to the exercise of any of their powers.
Some Ministerial approval for borrowing is required.
Appeal of licensing decisions is to the Board of Trade.
The Authority can act akin to a local or governmental authority.
The Authority can regulate others in a way that is over and above the way private companies can.
Having concluded that the Authority did exercise functions of public administration, the Tribunal then went on to look at the terms of the request and to which particular function the requested information related. The Tribunal then considered whether that particular function was one of public administration.