Join Date: Jul 2005
Location: London, ARN, HEL, ..... or MAN
Programs: BA GGL / GFL, Mucci Diamond!, HH Diamond, Radisson Premium, IHG Gold, Hertz Gold
Posts: 5,898
Hi - yes, lounge access for Sapphires and Emeralds is granted even for domestic flights on BA.
In T5, you'll have access to the First Class lounge (South Lounges). In MAN, there is a galleries lounge. As long as you're flying BA on both legs, you will get lounge access, assuming you have your card or if your number is already recognised in your booking.