I don't think it's that, considering he's standing down at the next election anyway:
He said he would not seek re-election to the House of Commons at the next general election. But, writing in the Observer, he says he envisages a role advising the Labour party on its policies on mental health while focusing more on his NHS work.
Whether that advisory role would be paid or not, I don't know, but it certainly wouldn't be to the tune of £90K!