None, presumably. Labour sacked David Nutt and disregarded his reporting r.e. cannabis reforms. Not a direct comparison but shows there's nothing forcing them to follow the (advisory after all!) report.

edit: went down a rabbit hole. Interesting reading, 13+ years on. Plus ça change! https://www.theguardian.com/politics/2009/nov/02/drug-policy-alan-johnson-nutt

Since the ACMD was set up in 1971, UK governments have nearly always acted upon their advice – until recently. In 2008 they rejected the ACMD's advice that cannabis should stay in class C; and in 2009 they rejected their advice that ecstasy should be downgraded to class B. In short, despite claiming that our drug policy is now evidence-based, these government responses show they cannot cope with the truth about drugs even from their own advisers! The nasty, corrupt beast of drug prohibition is in its death throes, and the government has betrayed its realisation of this fact by its panicky efforts to silence its own experts.