Does a separate mains spur for hifi make a difference?

I'm contemplating installing a separate mains spur for my hifi. I've avoided doing it because it'll be quite a hassle due to the layout of my house. I've been thinking of adding a spur to my Consumer Unit of 10mm2 mains cable to an unswitched single socket. For me, this will be a fairly expensive undertaking and I'm wondering if it is worth it.

Most of the time my hifi sounds okay, but after 11pm when the mains settles down it can sound a whole lot better. How much this improvement is due to the mains and how much due to my psychological state I don't know. So I'm curious:

1. If you've installed a separate mains spur for your hifi, what did you install?
2. Did installing a spur make your system sound better e.g. like the after 11pm effect?

P.S. I should point out that I wont be doing the work - I'll pay for a certified electrician to do it.

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