Whatever Sir Ian Blair says, the opposite is probably true. It's a basic working assumption that has at least one major advantage - that even when it's wrong, it won't lead you into anything too terrible. Rather like the Malatesta estimator. To estimate a value people disagree about accurately, take the most and least exaggerated values, total them, and divide by 2, then subtract 30 per cent. This last manoeuvre takes into account the fact that exaggeration has no limit, but underestimation can only go as far as zero.
Sir Ian is currently furious that one of the suspects in the murder of Bradford PC Sharon Beshenivsky apparently fled the country posing as a veiled woman. Why didn't the Immigration Service stop him, he wants to know? Subtext: if real men like Sir Ian were in charge, they would have been more offensive to brown people.
Unfortunately, the Immigration Service hasn't operated any embarkation controls for some time. When there is a APB out, police detectives are deployed at ports to look for the suspect. As he is believed to have passed through Heathrow, it's Sir Ian's very own Special Branch who missed the unusually hefty lass.