The title of these episodes is How Did Christianity Begin and the two guests in the studion co-wrote a book of the same title: http://www.amazon.co.uk/How-Did-Christianity-Begin-Non-believer/dp/0281058504
Undoubtedly, this collaboration helped them to discern precisely where they disagree about how we should best understand the gospels. They debate back and forth quite a bit, mostly about how these documents were developed over time, and to what extent they should be considered undiluted eyewitness reports rather than the result of decades of mythical accretions upon orally transmitted traditions about Jesus. They went into special detail on the Christology of Paul and John, as well as the gospel resurrection stories, such as the zombie apocalypse of Matthew 27.
Interestingly, these two Bible scholars are not at the extremes (Gospel inerrantist, Jesus myther) but much more toward in the middle, but still on opposite sides of a chasm that can only be crossed with a leap of faith.
Overall I'd say that these two episodes, taken together, are one of the best radio debates on whether the Christian gospels should be believed and why. Definitely worth your time if you find this subject of interest.