All companies in Guernsey must register with the Guernsey Registry. This also applies to most charities and NPOs. The Guernsey Registry maintain a registry of all companies, charities and all NPOs in Guernsey. These are recorded in a publicly searchable webpage database for companies and also two separate lists for charities and NPOs.
Please Note: According to OpenCorporates, the identifiers are not unique across the Guernsey Registry, as there a five separate registries that can be assigned to organisation information and up to five companies my have the same identifier. OC have thus added their own identifier number based on each registry type. Further details available here - qa_public/register_problems/guernsey
"All Guernsey companies must file an Annual Validation submission with the Registry during January 2017 (unless incorporated in December 2016). Submissions received after 31 January 2017 will be subject to a £100 late filing fee." 
"The Charities and Non Profit Organisation (Registration) (Guernsey) Law, 2008 requires all Non Profit organisations based in the Islands of Guernsey, Alderney, Herm and Jethou to register with the Office of the Registrar. A failure to do so is an offence.
However there is an exemption from this requirement. This applies to Non Profit organisations based in the Islands of Guernsey, Alderney, Herm and Jethou with gross assets and funds of less than £10,000, or gross annual income of less than £5,000."