I haven't found anything 100% conclusive online, but I believe this is John, not Paul, playing a Fender VI.
"Helter Skelter" isolated bass line
It certainly sounds that way--really inconsistent time, tons of fret noise, pulling notes sharp on the low E string (easy do on an instrument with such low string tension), and it just doesn't sound like Paul at all. What a mess! Raunchy! Fantastic! Music!