The code of practice which this link takes you to
http://www.ofcom.org.uk/advice/codes/s_m_cop_f ixed.pdf
only relates to companies trying to sell you their (fixed line) phone services. However, since it is approved by Ofcom, it would seem reasonable to assume that it is consistent with other regulations.
That code states "Discretion to be used when visiting consumers� homes, particularly during the hours of darkness. No face to face contact to be made outside the hours of 08.00 to 20.00, and no telephone calls to be made outside the hours of 08.00 to 21.00, unless at the customer�s request"
Chris