 HOUSEHOLDS should be prepared for further rises in their power bills of the magnitude of Scottish Power's inflation-busting 19pc increase in gas prices and 10pc hike in electricity tariffs, Centrica chairman Sir Roger Carr has warned.  Sir Roger, who is also president of the Confederation of British Industry, says in an interview with The Sunday Telegraph that last week's action by the Spanish-owned Scottish utility should not have come as a surprise as wholesale power prices have been rising by more than 20pc.  He say 