Magic Mouse scroll not responsive

Mouse works fine but for the scroll. It won't scroll horizontally or vertically. Sometimes I get a very slight vertical movement, but that's it. Right click is also temperamental. It appears to be trying to scroll the screen when not in use but moves only very slightly.

• All the accessibility and mouse settings are set to scroll.
• Still fails when connected to another mac that has a working magic mouse.
• Tried loads of different batteries.
• Battery terminals clean.
• Tried off and on, pairing and removing.
• Tried with single and multiple fingers.

Seems to be a hardware problem, but I don't know which part is failing to fix or replace it.