Go with your LMP dates darl, as all it takes is for the sonographers to be a little bit out in their measurements and you'll get completely different dates (and in those very early days of your first scan half a mm or 1mm can throw the dates out quite a bit).

BTW, I used to live in Sale too Not too bad a place to live, at least compared to the town I'm in now lol, we don't even have a Sam's Warehouse anymore