Why does Parliament have the power to impose taxes on the British colonies according to Grenville?

As prime Minister, George Grenville had to raise taxes, basically to be able to pay the army. The timing was not good to raise them in England, where violent protests took place against the tax known as cider tax. Grenville insisted that there was no question but that the British Government had an inherent right to tax its colonies. The idea was to tax through the Stamp Tax, which required an official stamp on most documents.