The BMJ published the Wakefield study, criticised it, and retracted it. They then argued that the Wakefield results they published were fradulent. Is BMJ reliable for biology studies or is it an anti vaccine conspiracy journal?
First: The infamous study by Wakefield et al., was published 1998 in Lancet, see here. Wakefield had indeed falsified his study, by selecting kids with certain preconditions, taking money from attorneys (and not disclosing it) and others. Here is a nice overview over it.
To your question: The British Journal of Medicine (BMJ) is indeed a reliable and credible source for scientific articles, as is Lancet. Journals can check the content they get for publication to some extend, but if they have authors which deliberately falsify studies, then they can do little. The thing which can be criticized in the Wakefield case is the time that it took to withdraw this publication.