Yes, Kat, I never did understand MOG....Well I'll go.... is a sort of exclaimation on the lines of 'well goodness me! Well bugger me! Will you look at that! I'm temporarily rendered incapable of speech by the unexpected revelation of what has just occurred!'
It doesn't actually mean you to go to the bottom of the stairs, but that's usually a good place to stand if you want to be hit in the arse by the postman posting magazines through the letterbox.
Enlightenend??
Morty, I do it too, and it shames me to realise I've been here over 2 years! All that time I could have been eating chocolate (and frequently was!!)
We've posted some crap between us ain't we!!
LTS