Art, I was in the London March too - it was seriously understated! Apart from the number of actual marchers who, as Ifor reported came from all walks of life, we were met by shop owners who offered us free drinks and food and received verbal support from many of the uniformed police who were stewarding the march.
Even conservative estimates from ariel photographs placed it at a million and a half; certainly many of the people I met also claimed they were there as "representatives" of others who were unable to make it for domestic reasons etc.