Scottish and Southern Energy has put its gas tariffs up by 9.4% just a day before the clocks go back and nights get darker. The new prices kick in from the start of December and will affect 3.6m customers.It is the first price rise by one of the 'big six' suppliers for two years and could pave the way for the other five suppliers to follow suit.The company blamed the increasing wholesale cost of buying gas which it said had gone up by 25% since March this year."The last few months have been marked by rising wholesale gas prices and, having absorbed losses in our gas supply business for some time, we can not delay an increase in retail prices any longer," said Alistair Phillips-Davies, of SSE."I am sorry it will take effect during the winter period."Using Ofgem's standard consumption measure, an average bill would go up by £5.60 a month rise, or £67 a year.The regulator warned earlier this year that prices would have to rise by £3 per year to meet an estimated £32bn upgrade to the UK 's ageing infrastructure.Other suppliers are being tipped to follow SSE's lead. "While we hope that other companies do not follow suit, history has shown us they adopt a pack mentality on pricing," said Audrey Gallacher, of watchdog Consumer Focus.Shares in the UK-quoted gas suppliers rose on the news with Centrica, SSE topping the FTSE 100 gainers at lunchtime.