Possible Clues:

• Month before Ireland could use this to raise old tax
• Switches company car going to Ireland, as this is the place where old duty must be paid on entry
• Old road tax is firm about odd riot
• Old Roman local levy (not derived from "eight")
• Old import tax
• Just one month in the year the French king could raise this tax
• After a month this might tax the king of France
• After a month that's one's duty to the king of France
• It's one's duty for one month at first, in short
• Tax the king in France after one month