In England: ground or air based heat pump?
A ground-source heap pump is a custom-made-site-specific piece of equipment, and as such, will be more expensive and failure-prone. On the plus side, it will be more energy-efficient than the compressor of an air-source heat pump system. With today's super-efficient air-source heat pumps, you'd be looking at a coefficient of performance (COP) of ≤ 3 for air-source and ≤ 4 for ground-source. Both are very good. In general, I would favor an air-source heat pump due to lower upfront costs, higher reliability, and greater ease of maintenance and replacement.

But the real question for your situation will be distribution. You say you're installing central heat and are talking about heat pumps; I assume this means you'll be adding ducts. But even with ducts for distribution, a victorian house with a lot of small rooms and multiple stories will be much more comfortable to heat using modern equipment if you also super-insulate it. You should pay very close attention to your air-sealing and insulation details, and budget more than you think for this.  And buy better windows than you think you need. Definitely triple pane. Better to spend more on the building envelope and less on mechanical equipment than the reverse!

If you want to be "net zero" you need all your mechanicals to be electric (no gas or oil), and you'll want to keep your interior electric load as low as possible. LED lights, no huge plasma TVs, etc. And you'll need a lot of solar PV to generate the electricity required to run everything. In cloudy England, that will be quite a lot! To deal with this, you might want to look into solar-trackers, per-panel micro-inverters, and even residential wind turbines. You'll need to have a net metering arrangement with your municipal electric company/service as well.