Hi, it looks like Wisteria crown gall, caused by a bacteria, which remains in the ground for about 2 years after the plant has been removed, google Wisteria crown gall, Derek.

You sure its wisteria crown gall, Derekm? Only it looks rather like Wisteria scale to me - confined to London and the south currently - these ones show no sign of white deposits, but that could be the time of year

https://www.rhs.org.uk/advice/profile?pid=508

Hi Bamboo, you could be right, wisteria crown gall looks very similar while it's young, so yes it could be W scale, my eyes are not what they used to be, Derek.

I;ve never actually seen crown gall or scale on Wisteria myself - its just these bumps made me think of scale on grapevines, so that;s why I checked if there was one which affected Wisteria...

Will it damage the plant

Read the rhs link given above on wisteria scale for what to do... and if its crown gall, you would do well to remove the plant completely because the infection is at the root, despite the aerial symptoms.

Thankyou to all who answered my question I am very grateful