Thanks everyone.
The piano is wood & string. When purchased it was quite a bit off. So we got a piano tuner in. However he chose to "clean up the tuning" rather than tune it accurately.
There was no pressure on him to do anything else. Just to make it sound OK.
So it was a cheap tune as we did not know how much it would be used if at all.
Now that we have progressed to BIAB for backing tracks we are paying the price.
A proper tune will cost a bunch and so at the moment something to avoid if we can tune the backing tracks to match the piano.

You have given us plenty of things to try.
We have Audacity and that seems to do the job so far.
So thanks to all.