I'm not sure that where the requirements are kept, in which legislation--whether it's the Identification of Criminals Act, the DNA Identification Act, or the Criminal Code--will change the process. In essence I think where it's up to the discretion of the police as to what type of sample to take, they can take blood, buccal, or hair. Hair, I believe, has a 5% error rate, and its use is discouraged, but there are cases when the police at the time should use their discretion to determine whether or not it's appropriate to take blood. There are medical conditions, such as for people who have had blood marrow bone marrow transplants, or there could be a contamination aspect.
On February 24th, 2009. See this statement in context.