A lot of people on this site have serious reservations about speaking to journalists, there have been many occasions in the past where a journalist convinced BLers to be interviewed under the guise the information would be presented in a factual and non biased way, something that rarely pans out to be the case.
I am not saying that all journalists do this of course, but it may help your credibility to elaborate on exactly what you want to find out and the angle that you are reporting on it from.
I couldn't live further from London and legal highs/RC's are the one class of drugs I have next to no experience with, so I am not a potential candidate, I just thought it was worth pointing out that if you want to get anywhere here a little more information could go a long way.