Not in British law. The law refers to possession, and it has been established in a case where a man admitted to swallowing illegal drugs that he was no longer in possession, even after the police had his stomach pumped and the contents analysed. The judge said that the man was no more in possession of the drug than someone would be in possession of glass of whisky after they had drunk it.

PS. I have had an email to say that this does not apply in Sweden, and that the police can and do raid parties; force people to have blood tests, and arrest them for possession if illicit drugs are found in their blood.