Is drinking say 4/5/6 pints in a night once every couple weeks (virtually sober all other days) whilst on accutane likely to be alright? clearly i am not looking for encouragement but rather an honest reflection of the risks?

The facts are this. The liver uses a specific de-toxification pathway to eliminate alcohol. That pathway can be altered/injured by Accutane allowing it to become overwhelmed. Injury to liver tissue is possible, but the liver can re-generate some lost tissue. If you are on Accutane the doc should follow your liver enzymes. If they do not elevate after drinking you are probably okay.

Alcohol is a poison that never did anybody any good, ever, so stay away from it. It will destroy your brain cells, damage testicular cells that make testosterone, facilitate development of cancer in many organs, cause hepatitis, cirrhosis and pancreatitis etc. There is no safe level of alcohol intake. Quit while you are ahead.