Qatar's Bu Samra, which can carry 265,000 cubic metres of LNG, is the first Q-Max tanker to arrive at the terminal in Kent since a new jetty allowed them to dock in December 2010.
"Liquefied natural gas will play an increasingly important role in helping to meet the UK's future energy needs," Centrica Energy Managing Director Mark Hanafin said in a statement.
"It's vital that we have terminals like this that have the capability to receive large carriers such as the Q-Max."
Centrica (CNA.L), the owner of British Gas, signed a deal in February with Qatargas, to be finalised this week, to buy 2.4 million tonnes of LNG a year via the Isle of Grain. [ID:nLDE71M0X8]
A spokeswoman for Centrica said the Bu Samra cargo was not one of the 20-25 cargoes that it expected to receive this year under the Qatargas deal.
Those deliveries will start in the next few months, she said.
Qatargas is already Britain's biggest LNG supplier through its South Hook import terminal in Wales, and the contract to supply Britain's biggest energy retailer boosts the small Middle Eastern country's share in Europe's biggest gas market.
The Isle of Grain terminal can supply 20 percent of annual UK gas demand.