"Marq" wrote
Am I right in thinking that Ph will differ year to year depending on how I
treat the soil with organic matter I add?

That is correct and don't forget the acid rain.

Another one he
On one of my plots where I am going to sow peas and a few brassicas, it
was
at the edge of a lawn and I turned the grass upsideside down last autumn.

Should I remove the sods or just get a nice tilth on the upper 2-4" and
hope for the best.(brassicas will be plants peas will be seed)

I know all brassicas like firm ground but personally I've always properly
dug where brassicas and peas are to be planted, the brassicas will probably
need some lime added to the soil anyway to bring the pH slightly above 7
(neutral). Peas are not that fussy with the pH IME.
I would remove the sods and stack them for more rotting and dig your plot
properly, adding some good well rotted farmyard manure (no straw showing) if
you can get hold of some.
You may have a few ground pest problems the first year if the plot was
recently grass but it will go away after that.

--
Regards
Bob Hobden
W.of London. UK