The UK CAA, if that is whom you are talking about, is an independent public authority, responsible to the Sectary of State for enacting the rules and regulations of the ANO.
The ANO is now a composite of legislative work, it forms basic UK compliance to the Chicago Convention which incidentally according to the European Unions Treaty of Rome is more superior to European Union law; since the UK government is a signatory to the European Union and has delegated certain responsibilities to the EU, who in turn have delegated it to EASA, means that the ANO or some other legislative work, is required reflect EASA regulations and directives, which cannot be contrary to the Chicago Convention.
So depending on what your problem is, and who it is with depends on who you may need to talk too, but the UK Sectary of State is the most senior person in the UK to talk too.