This list is valid for Inter-Rail passholders, but is probably also good for Eurail passholders (subject to confirmation), since the conditions for both passes are becoming more aligned.

Lounge access is specifically not allowed in Germany (DB). The list doesn't mention the UK, where conditions may vary between train operating companies (TOCs). I have never had any problem accessing a Virgin Trains lounge with an Inter-Rail pass, but haven't had experience of other TOCs.