By Emma Mackenzie When Kate and William were filmed by a member of the public at a farm shop near their Windsor Home of Adelaide Cottage last weekend, it should have put speculation over the Princess of Wales’ whereabouts to rest, but even high-profile figures have expressed their doubts over the veracity of the video. Rachel Johnson \- the sister of former Prime Minister Boris Johnson \- has claimed that after noticing what she believed to be a “few red flags” in the video, she struggled to believe that she was really seeing Kate walking and carrying a shopping bag. The columnist was even lef…