Britain decided to increase income tax on the top one percent of taxpayers to fifty percent. Predictably, revenues from the top one percent of tax payers collapsed.
This demonstrates the entirely unsurprising fact that a income tax of 50% plus VAT tax of 20% for an effective tax of 60%, is well above the Laffer limit.
I doubt that this came as any surprise to those imposing the tax. More likely the tax was imposed for political reasons, so that heavily taxed poor people would spitefully and self destructively vote for high taxes because rich people are taxed even more.