Originally Posted by MarkXS

As a CO Gold you'll be Star Alliance Gold. That gets you free access to any *A Gold lounge when departing on any *A carrier. You can use the AC/SK "London Lounge" if flying CO out of T3. If SQ is still in T3 (don't recall) you can also use their smaller but very nice lounge as well. If CO moves to T1, which I'm sure will happen sooner or later, then the shared *A Lounge and the separate BD lounge are available.