Quite possibly. But still a fair example of the principle, if not the current reality.The RN - At current strength, does not have the capacity to protect the UK's supply lines
Perhaps that is for another thread.
Others are not always available and it may be very much in the national interest to look to ensure supplies.Poor example: throughout the Battle of the Atlantic the Americans were both supplying Britain ( and those allies based there) and building up equipment depots for their own use, so it was mutually beneficial for both Britain and US/ Canada to jointly protect convoys.
With regard to today's trade routes, we are not at war, it is therefore the suppliers' problem to ensure their goods reach destination, not the buyers'. As in most trade, if one supplier is unable to meet contract, others are available.
Your scenario would have UK forces eternally deployed doing what supplying nations should have been doing in the first place. Which rather negates any benefit of trade with such countries.