It was a clear illustration of the perils of investigative journalism. At 20.45 last night, a full fifteen minutes into the programme, the electronic programme guide still declared that last night's edition of Panorama would be dedicated to an investigation of Lord Ashcroft's financial affairs. The documentary had been heavily trailed. It was not what the BBC actually transmitted. Following some late fact checking a discrepancy in the evidence emerged and a late decision was taken to replace the advertised edition. This story from Media Guardian explains what happened.