In formal letter writing, what is the normal representation of the date?

The representation of the date in formal letter writing typically adheres to conventions that prioritize clarity and professionalism. The option "3rd February 2018" follows the British English format, where the day precedes the month, and the inclusion of "rd" indicates that the date is the third day of the month. This format is easily understandable and widely accepted in formal contexts, making it appropriate for formal letters.

The use of the full month name also adds to the clarity and formality of the date, reducing any potential confusion that might arise from numerical formats, especially in international communications, where date formats can vary significantly. This choice also aligns with professional standards in written correspondence, ensuring that the date is presented in a clear and respectful manner.