Waterbear and Merecat have covered the main points very well.

An accredited course guarantees BACP membership if you apply/pay for it and the extra hours and evidence that Merecat mentions are the route to accreditation.

As Merecat rightly points out, hours doesn't mean competence but at least with a professional organisation there is an ethical framework to uphold and be accountable to. You've had really accurate and helpful responses here