Politician attending debauched event with fellow countryman (10)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

MP (Politician) inside COAT (?? I cannot explain this??) , then RIOT (debauched event) From Comment #2: CO (fellow) MP (Politician) AT RIOT (debauched event) I also removed underlining from “fellow” – not part of the def.