From a netfriend:

I first enountered John Stott at a mission to Wits University, (South Africa?) which lasted a week. The Rationalist Society was along at every meeting to heckle, and handing out tracts at the door, such as Bertrand Russell’s “Why I am not a Christian”.

John Stott dealt with their questions straightforwardly and courteously, and though I don’t think he had won any converts from among the hard-core rationalists at the end of the mission, I think he won their genuine, if grudging respect.