"Any idea what Wikileaks exposure of Lord Arbuthnot was about?"
No, and it may be nothing more than a citing of his name on leaked documents rather than exposing personal corruption or crimes; either way a clear conflict of interests for his wife, Judge Arbuthnot.
Interestingly she was reluctantly forced to eventually recuse herself in 2008 over a Uber case, because of her husband's business dealings with Uber.
I did find mention of another case where she was forced to recuse herself, "after being outed as a pro-Israel stooge" !: