I's not clear, but my interpretation is that they'd called him & began the meeting with "We'd like to discuss your salary; we see your compensation is at 10%"; without making it clear that they were planning to lower it. The clerk pre-empted their plan to lower it; but tactically said "I'd not take a penny more from you" to imply that he'd assumed they were about to offer him more. By this action, he's shown that he's not going to be greedy & take more even if offered, which puts the silks in an awkward situation where to correct him & say that they meant to lower it would be rude given he'd "so generously" declined the fictional offer of a pay rise.

Thank you, that interpretation was the one that made the most sense to me, too. But I figured I might be missing some context from British culture or class dynamics.

"I’m not going to take a penny more from you"

A penny being the smallest unit of currency. So he's simply stating that he'll not take any more money in recognition of the fact that he was very well compensated.

This implicitly discounts the possibility to reduce the amount of money he'd take - and so if that's something the barristers wanted to do they'd have to explicitly bring it up. Which, I think we can all agree, would be simply too awful to contemplate.

I saw this as a veiled threat from the Clerk that they'd drop the barristers as clients - in other words the clerk wouldn't ask for a penny more compensation because he wouldn't be passing the barristers any more work.

Indeed. And in this veiled threat contained a promise that as long as the fee [10%] was paid, the Clerk would continue to work without problem or hassle.

In making so, the cost/risk of the Clerk was minimised compared, in modern language, to changing vendor. There were no more hidden costs.

No idea why you were downvoted.

That's an interesting interpretation that did not occur to me. Thanks!

My interpretation:

He said "I'm not going to take a penny more [than 10%] from you."

They heard "I'm not going to take a penny more [than all the money I have already taken] from you."

They were too polite to press the case once the misunderstanding became apparent.

And thanks for the downvote, keep making sure no good deed goes unpunished.

Just for the record - that wasn't me.