You have a right in law to declare Cornish as your National Identity!
On 4th June, 2018, Steve Double MP for St Austell & Newquay said in a letter written to the Grand Bard of Gorseth Kernow, Dr. Merv Davey:
“The Cornish identity and language are indeed distinct from other identities and languages in the UK, and I am glad that the Council of Europe paved the way towards proper recognition of Cornish cultural identity and linguistic distinctiveness.