Commutation Act

The Commutation Act of 1784 was a law passed in Britain to lower tariffs on tea. An academic article on the act begins by stating:  "By lowering duties so as to remove the incentive for smuggling, the Commutation Act of 1784 marks a turning-point in the history of British tea trade."
  Up until that time, more tea had been smuggled into the country than had been imported legally.  The law reduced the tax from 119% to just 12 1/2 %.  "The smuggling of tea ceased to be profitable, and the smuggling trade vanished virtually overnight." 
Prime Minister  William Pitt the Younger had led the effort to get the law passed.  He had been supported by tea dealers.  The law also affected the monopolistic power of the legal importer, the East India Company, giving domestic dealers more power in the trade.  

References

Category:United Kingdom law