Should you read back the QNH from an ATIS broadcast?
Uk CAA CAP493 Section 3 Chapter 1 Paragraph 11.4 states :


  In the case of a departure ATIS, controllers must obtain a read-back of all relevant altimeter settings contained in the broadcast, unless the setting will also be passed in association with start-up or taxi clearance.


So from the point of view of the controller you are doing a good thing because you are saving him the expense of having to confirm that you have the right QNH on board.