"We are committed to providing the best possible prices for customers," he said.
"This price cut will go some way to helping customers manage their budgets, and we will continue to do what we can, when we can."
Watchdog Consumer Focus welcomed the price cut, saying British Gas had "done the right thing".
But chief executive Ed Mayo added: "There are millions of electricity-only customers that will not see a penny off their bill.
"We will now turn the heat up on the other five companies that are keeping prices sky-high."
It's going to give some customers a bit of respite at a time of year when they are are going to be spending significant amount on heating their homes
Tim Wolfenden, USwitch.com
Meanwhile, Age Concern said that, unless there were further price cuts from all suppliers across all tariffs, "many of the poorest pensioners will continue struggle to pay their energy bills".
"Even with price decreases, millions of the poorest pensioners and families will still be living in fuel poverty and will continue to pay more for their energy than wealthier customers," said the charity's director, Gordon Lishman.
The cost of wholesale gas is linked to the price of oil, which has fallen significantly from the peak it reached in summer 2008.
Frankly it would be more realistic to reward customers who manage to pay their bills at all, let alone before the due date arrives
Rob Ridge Simply Switch
Mr Mayo said: "Consumers would not have to rely on occasional grand gestures by energy companies if the market was more transparent and competitive in the link between wholesale and retail prices."
British Gas's move was a "positive first step" towards lower prices, said Tim Wolfenden, head of home services at price comparison website USwitch.com.
"It's going to give some customers a bit of respite at a time of year when they are going to be spending a significant amount on heating their homes," he said.
But he added that by only cutting gas prices and leaving electricity alone, the move suggested suppliers were feeling "very cautious".
"Energy price cuts are likely to be too little and too late to help consumers with this winter's fuel bills. More importantly, it is now looking highly unlikely that price cuts are going to wipe out last year's painful hike in household energy bills."
Other firms were likely to cut prices fairly swiftly, Mr Wolfenden added.
And he urged people to see whether they could get a better deal on their energy bills - especially if they had never swapped supplier before.
British Gas is also offering a £15 annual discount for people who pay their bills promptly.
But Rob Ridge of comparison website Simply Switch said that idea was "particularly galling given the pressure household finances are under".
"Frankly it would be more realistic to reward customers who manage to pay their bills at all, let alone before the due date arrives."
At the beginning of January, Scottish Power, one of the major suppliers, said it was relaunching one of its fixed-price gas products with a reduction of 10%.
Consumer gas prices*
*Paying by quarterly cash or cheque. Based on 20,500kwh including VAT. Source: Consumer Focus
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