I think you are getting confused between RM and RN.
Officers in the Royal Marines come under the army list and ranking system.
No warrant rank in the British Army has held Commissioned Officer statis [Conductor highest grade].
Unlike the Royal Navy, the like of Engineers and Chief Carpenter's were firstly given warrant rank, later been given Commission statis [ it was thought that anyone who worked for a living couldn't possibly be of Officer class].
In 1949 the warrant officer became Branch Officer, the commissioned warrant officer becoming a senior commissioned officer and the warrant officer a commissioned officer.
In 1957 these officers became special duty officers. The senior commissioned officer became a lieutenant and the commissioned officer a sub-lieutenant.
The warrant officers were first granted higher rank in 1865 with the title of Chief etc.
Midshipmen were classed as Subordinate Officers along with Naval Cadets and Clerks
As for Aspirant, the term in Europe implied a soldier or senior NCO training to be an officer.
In general warrant officers commissiond or not, are not training to be officers, so I don't think the term Aspiant fits at all for these ranks.
Also to compare police and fire dept. ranks to military ranks is bound to confuse the issue. How many small town fire and police chiefs walk around with four stars on the shoulder, while commanding a dozen staff.
If the ranks don't translate, keep the original name and go by the style of the uniform and insignia to classify statis.
Other than that, if he's proped up on the bar of the officers mess, chances are he's rated an officer [Aspirant not withstanding].
Sorry about the long reply