CalZed, worst case senario I have a UK Spec 45,000 mile engine here still running in the car which you could buy off me if needed  
If it's a loud knock and getting worse chances are it's bottom end.  
  
I would check all levels on the car, drain tank and fill with fresh fuel before running. Fingers crossed for you that its not as major as I have suggested. As said above get someone who knows what they are looking at to diagnose first. 
  
Best of luck