Thank you for reaching out to us @Tony_Potts . I would be happy to try and assist.
Here is a link with our UK compatibility page and our compatibility checker tool: https://bit.ly/368gqlJ;. We don't need to check the wiring generally for the EU model, this is just for the US one. We would go based on the type of boiler you have.
Since you have a zoned system the thermostat will be connected to the zone valve most likely, so there should not be an issue installing it. You can also have a look at this installation video to get an idea on how it should go: https://bit.ly/2X5uDbn .
From the looks of it, the wiring you have there should be ok. You will use the live wire from L and connect it to the C terminal on the Google Nest E Heat Link. The wire in the N terminal you will be capped off, as we don't require the neutral wire. The wire in the On terminal is most likely your call for heat wire and that will go in the N0 terminal on the Heat Link.
However if needed, do check with an installer if needed to confirm this is the case, to be safe. It does however seem that this would be the configuration for your system.
