Most of the PW is within a couple of miles of "civilisation" at the most - apart from the Cheviot section which is a bit emptier.
Wild camping in England isnt legal wthout explicit permission from the landowner. This , however, is widely ignored and it is practically possible to wild camp for all of the PW.
The main strategies in England are to camp discreetly and to pitch late and leave early. In Kielder, the forestry commission have dedicated wild camping spots and when you hit the Scottish Border you can wild camp legally on the Scottish side - which is drier than the English side anyway and has better places to camp
In the South Penninesd, you might have difficulty in finding drinkable water because there is a lot of mineral pollution, specially iron oxides - or is, in effect, bog water on the PW itself.
In addition to "wild" camping spots, there's also some informal spots where you can camp with permission or by payment of a small fee - these are usually pub or B&B gardens or paddocks.
I camped wild quite near jct22 of the M62, in South Tynedale and in the Cheviots and used a back garden at Byrness - and campsites at Edale, Crowden, Hebden Bridge (New Delight) , Ickornshaw, Horton in Ribblesdale and Dufton - a bunkhouse on Hadrians Wall, a YHA at Baldersdale (now closed), Pubs/B&B at Gargrave, Malham and Langdon Beck and a friend's floor at Nenthead (off route!).
All of the campsites were very quiet.