[Zippy]

My Pentland Javelin have come out not only scabby, but with weird potato growths (see pic).  My other FE were really clean in a bed next door to these so I think it may have been the seed potatoes rather than the soil as I treated both the same way.

These are the worst ones - most are eatable if peeled.

Any ideas? Is it not scab but something else?

[Trillium]

Some varieties are specific with knobby growth, which are a bit harder to peel but often have better flavour. Looks like the PJ seed somehow crossed with another type, one with the growths, and this is what you got. Scab is mostly a soil disease but can be controlled by regular rotation. Most likely your next seed potatoes will be true to type.

[mumofstig]

Is it just potato flesh inside the bumps?

The do look a bit like Pink Fir Apple spuds, but also as if they have some kind of gall 

[Swing Swang]

If the flesh is OK I wouldn't worry about them, as the galls and scab will come off with normal peeling. Scab is more likely to occur in alkaline soils and a little bit of brimstone on next years ridges might help, although it would be wise to check soil pH first.