being off grid
I appreciate of course that there are lots of variables, tree coverage, cloud cover, snow cover etc etc. However all other things being equal and assuming for the sake of chaos an approximately east west orientation (if that actually makes a difference). How much PV would you want to put on your roof, to ensure that you never had to pull from the grid even on an averagely dull day.
Lets assume for the sake of removing some more variables also, that you don't have an electric car to charge,
I doubt you could do it with just PV, TBH, as there will be periods in winter when you get several days in a row with virtually no generation, and even when you do get some generation in winter it's unlikely to be enough to top up any battery system so that you can ride out the poor generation days.
Combining some wind generation might get you there, but in middle England I think even then you'd struggle, and would end up relying on a generator for a few weeks in the year.