The advice thus far has been pretty much common sense TBH but it's still appreciated! Once I've got past my introductory sessions he said he'll tell me a bit more to progress.
Because I'm so unfit, he said to try and find somewhere flat to start off with - a playing field is ideal so I go to the one just off the Lea Vale Road/Albermarle Road/Melrose Avenue estate (if you know Norton?). It's about a mile to get there which - depending on my mood - I either walk to warm up or run if I'm feeling adventurous. No big hills as they'll $#@! you up if you're not used to them. He also advised walking at least some of the way back to act as a warm down.
Also - don't run every day because you'll burn out. I've done Sun, Tues, Wed, Fri this week. And will do one tomorrow. So 2 days on, 1 day off.
I do roughly 3.2 miles which works out at just over 5k. And I'm now able to run just about all of it without utterly destroying myself. I think that's pretty good for just over a week. The best thing about it is now I'm back home and sat down, I don't feel in pain, I get a nice mild ache which tells me I've done something good! I was in agony after my first 2.