Thanks again for your helpful comments, you have no idea how much this is appreciated. Andrew, you sir are an absolute legend, spending the time to create a how to document such as that referenced. I have no hesitation in taking on the fuel pump mod you have suggested thanks to your guide.
I wasn't even aware of how to access the 'hidden menu' until reading through so i've already learnt something new, let alone now beginning to understand how and why the X5 fuel tank is the way it is.