Just remembered I'd asked in here, so I thought I'd let you know what happened.
I went to the GP and got a referral for physio triage, but whilst waiting for this my knee gave way, twice, on bending. I ended up being referred to the Orthopaedic clinic via Accident and Emergency and this lead to anMRI scan last October.
Following that, it showed a 2 cm defect at the femoral condyle which continued to give me quite bad pain on mobilisation, weakness and clicking right through January.
I was lucky enough to get a cancellation slot for an arthroscopy and microfracture procedure which was uneventful. I'm now 3 weeks into my recovery none weightbearing