Some recent case law from the UK:
Dr Ranger twice sought to be appointed to the House of Lords as a non-party-political life peer, both times without success. He brought a claim for disclosure of two letters sent by third parties to the House of Lords Appointment Commission concerning his application. He asserted that he had a right to see the letters under section 7 of the Data Protection Act (UK) 1998. He also sought material produced by the Commission in considering his application. The UK High Court dismissed the claim, based on the exemption in s37 of the Act for personal data processed for the purposes of “the conferring by the Crown of any honour or dignity”.
Two points may be of general interest:
First, although not determinative of the case, the Court expressed doubt over whether the letters would necessarily be regarded as containing “personal data” merely because they expressed views on Dr. Ranger’s application. The Court referred to the previous High Court decision in Durant v Financial Services Authority  EWCA Civ 1746, holding that “mere mention of the data requester in a document held by the data controller does not necessarily amount to [personal data under section 7 of the Act]“.
Second, the Court rejected arguments that the exemption in s37 was disproportionate and therefore not “a necessary measure to safeguard the protection of the rights and freedoms of others” permitted by the Data Protection Directive 95/46/EU. In doing so, the Court explicitly recognised the need to protect the privacy interests of those submitting information in confidence, as well as the broader public interest in encouraging full and candid submissions to the House of Lords Appointment Commission.
Link (BAILII): Ranger v House of Lords  1 WLR 4324