Sick pay advice needed badly

My husband has been working for the same company for 5 years and he a permanent resident. As of March last year he was diagnosed with 3 discs needing to be replaced in his lower spine. Due to the pain he has been on sick leave since then. He has taken all the sick leave payments accumilated to him since then and taken a couple of months no paid leave. The medical insurance doesn't cover the cost of an operation which involves 2 surgens and 8 hours op. He is now unger Queen Mary and expected to have the op around March time. The problem now is that he has too resume work as our finances are non existant. The company are now saying that for legal reasons he has to have a medical assesment to say he can resume his his duties, which of course he can't really but we need the salary. Can anyone offer any advice on what to do and if there is any way of still getting sick pay.

Sorry for the long winded email.

please Advice

CurlySue