I was stopped by the Police and I was shocked to find out that I was driving uninsured. Apparently my insurance Policy expired a week ago, but my insurance company failed to inform me. What can I do as this was an innocent mistake on my behalf as I would never knowingly drive with no insurance?

You will be convicted of the offence.  There is an absolute requirement for vehicles to be insured and the obligation puts the onus on the driver and keeper of the vehicle.  Whilst the error would not have occurred deliberately, the circumstances amount to mitigation, not a defence.  The potential punishment is a fine plus 6-8 penalty points or a driving ban. 

Whilst you have our sympathy in what is becoming an increasing problem, the difficulty is, although you have been let down by your insurers, that does not negate your obligation.