I am a trainee coming up to qualification. I have signed a contract for a role at my current firm but now have a much better offer from another firm. The contract commencement date is September and there is a three-month notice period (“…the employment shall commence on the commencement date and shall continue until terminated by either party giving to the other not less than three calendar months notice”).

Do I have to wait until I start in September to serve notice or can I serve notice before the contract commences?