Tourism and there tax returns at a guess
That's not quantifiable evidence.
One of the royals did a local vist near us the town was packed out shop cafes pubs full and chargeable carpers full due to royal visit brought a lot of money into our town that day
But that's just one tiny piece of the puzzle. People may have spent that weekend, but cut back for the next few. Spending may have been up in your town but down in all surrounding towns. Would a minor celeb (who the tax payer doesn't fund) have had the same effect?
It's not helpful to take one thing in isolation, you need to look at the bigger picture .