Mouse, rat, fiddler, piper, tinker and fool - as well as lord - have all been used over the centuries to complete the phrase "as drunk as a..." Fiddlers, for example, were supposedly not paid in money at inns but had as much to drink as they could cope with. As a result, they often ended up plastered. In the case of lords, it may well have related to the fact that they were rich and therefore best able to buy sufficient qauntities of alcohol to end up in the same state.