I have had letter from BT detailing the new price changes in April 2008. The letter lists some of the changes to the price plans. In the terms & conditions it states that evening call prices will change from 4.5p for 1 hour to 1.5p per minute plus a 6p connection fee. This increase means that a 1 hour call on Option 1 will increase from 4.5p to 96p.
BT fail to mention this in the letter, you have to read the terms and conditions to find this information.
If you are on option 1 and make a lot of evening calls then your bill will go up substantially