Yes, a fine house will require a higher spec of plastering, floorboarding, carpets fitting back, skirting boards, paintings and ornaments casing and protecting, chandeliers sheeting off and cleaning, and more time pulling in longer cable runs and cutting neatly into oak panels. And not forgetting heating management system, electric gates, garden lighting, cctv and security system, home network cabling system, and maybe a dist board feeding final circuits and or a consumer unit on each floor.
Unlike a standard back to back or 3 bed semi, where the occupants are on a mimimum wage and anything over £1600.00 is too much.
The last rewire/extension that I did on a fine house around 8 years ago, was a 3 bed semi within its own grounds converted into a 6 bed with en suites and a guest bathroom, when I finally finished it. The final bill was around £14000.00, twice the original ball part estimate that I quoted due to the amount of work and time it took to get the standard agreed. Despite them getting quotes of between £3500.00 - £5000.00, I ended up doing all their work on their other properties and warehouses that they owned. Then I was asked to do their air conditioning in their offices and new home as they had heard of heat pumps, and their potential efficiency. But that's another story.