Immigrationboards.com

I want to apply for a British passport (first application) but I want the spelling of my surname to be slightly different from how it appears on both my certificate of naturalization when I was given the British citizenship and my EU passport.
The difference is a minor one, change of a letter only. For example from Nikolas to Nicolas, ie the -k becomes -c. Same sound but different letter.

Does anyone know how to do this please?

I think it would be best you get your British passport with the name as is per certificate and foreign passport. Then change the name by deed poll and apply for a new British passport. HMPO insist that your name on the British passport is the same as on certificate and foreign passport. Applying for deed poll and new passport is then a totally separate exercise. https://www.gov.uk/change-name-deed-poll