I know on the BA board they mentioned this already, but just in case you don't know. I received the following from CX:

New rules for hand baggage from 7 January 2008

From 7 January 2008, the following hand baggage restrictions will apply for travel through security control at Heathrow airport.

For passengers travelling in the economy sections of aircraft, the allowance will be to take ONE item (25cmx45cmx56cm) of hand baggage through security control, plus ONE additional personal item.

For passengers travelling in premium cabins - business or first class cabins - the allowance will be to take TWO items (25cmx45cmx56cm) of hand baggage through security control, plus ONE additional personal item.

Definition of a personal item
In addition to their carry-on bag(s), customers may bring ONE personal item, which includes a purse, briefcase, laptop or baby changing bag. Laptops in a thin satchel and slim line briefcases are considered a personal item; however laptops in larger computer bags and larger, bulkier briefcases are counted as one piece of hand baggage. Passengers should be advised to check with their airline, since additional restrictions may be applied by airlines in line with their own operating procedures.

Security Guidelines
The BAA website provides further details of the security guidelines that apply. The other restrictions that currently apply under legislation have not been varied by this instruction and will continue to apply, including the 100ml liquids rule, whereby liquid items may only be carried in containers holding up to 100ml and must be carried separately in a single, transparent, re-sealable plastic bag. For the avoidance of doubt such a bag will not count towards the bag count outlined above.