A proposed explanation for the pronunciation 'leftenant'

Why is lieutenant pronounced 'leftenant' in British usage?

The proposed answer links the senior lieutenant with a place on the commander's left, but the exchange provides no evidence establishing that etymology.

The difference between 'lieutenant' and the British pronunciation 'leftenant' prompts a proposed explanation based on where an officer stood. One participant associates the senior lieutenant with the captain's left and the senior NCO with the right. The explanation distinguishes a rank from a particular position beside the commander. No linguistic or documentary evidence is offered for that origin, so it remains a recollected explanation within the conversation.