As at early 2021, the situation was that Midland Quarry Products were actively operating in the upper quarry, and the workings were approaching the lower quarry with an intent to re-open that for commercial use. They were also using the pool in the lower quarry to store surplus run-off rainwater etc from the upper quarry, so to all intents they consider the lower section to be ‘active workings', which means that it's within the exemptions provided for in the CRoW act, despite being on land mapped as CRoW some years previously.
In early 2025, the BMC is still trying to confirm whether the above still applies, but for the moment please do not try to access the lower quarry area.