Big Dick Edwards, you are right. One of the West Ham main hooligans, Bill Gardner, was either a steward or had got himself a steward's jacket for the day. He let 100+ ICF blokes in and it just kicked off all afternoon in a Vietnam style ambush. Most Villa fans who went to that game either got some aggro or a very close observation of it. Horrible.
Very rarely talked about is the revenge from Villa. West Ham played at Blues at either Easter or May bank holiday whilst we were away to Man City. We had a ridiculously small away following as loads of Villa fans were at New St waiting for ICF. And at first hand I saw the most violent, angry Villa mob I have ever seen when we played the Hammers at home in October 1981, our first encounter since that cup game. Everybody under the age of 40 seemed to go mental and a lot of West Ham fans took some very serious hidings - it really was brutal. The fighting seemed to go on for an hour and around 60 Villa fans were arrested.