The guy that has been looking at it after replacing 2 brake switches says it has to be the handbrake switch, just wanted people's thoughts as I didn't want to get the EPB switch and then it turns out not to be that, the way you've described it there though, then maybe it is

What was the original fault code, before the first switch was changed.

Although I have not got a description or manual for the EPB, I am sure that all kinds of inputs feed into the handbrake controller to decide when it will apply and release. For example footbrake, accelerator, yaw/acceleration sensors, etc.

Also what is the exact model/configuration of your FL2, (is it an auto) FL2 XS SD4 Auto 2010 2012-2017 (21k - 91k miles) (MY2011)
FL2 Metropolis SD4 Auto 2014 2017- (16k - 79k+ miles) (MY2015)
Metro in its 11th Year of (Extended) LR Warranty / Full LR Service History
(Expensive, but Trouble/Worry free - hopefully?)

It's a 64 plate HS auto

I'm not sure if we have covered this before, but if you look at this PDF Diagram of the EPB Cct you will see that the switch has its own Grounding Point G3D127-1. This is situated on RH side of vehicle and has 2 joints in it plus the plug and socket. Might be worth having a look at this.
Also why I asked what the original fault was - I did wonder if something was disturbed or damaged whilst the first switch was changed, and is now the cause of the fault.
The 2nd PDF Diagram show the earthing layout, you can see that the EPB switch shares its earth with the 12v sockets, Terrain Response Switch and (one of ) the Heated Seats. (this could be LHD diagram?) Therefore some other things to check function of.

https://www.freel2.com/gallery/albums/userpics/23008/Electronic%20Parking%20Brake%20Diagram.pdf

https://www.freel2.com/gallery/albums/userpics/23008/Electronic%20Parking%20Brake%20Earthing%20Diagram.pdf






PS -- Does anyone know of a reliable copy of the MY2013 onwards Workshop/Repair Manual with a good write up of how these functions work and what are the operating characteristics. FL2 XS SD4 Auto 2010 2012-2017 (21k - 91k miles) (MY2011)
FL2 Metropolis SD4 Auto 2014 2017- (16k - 79k+ miles) (MY2015)
Metro in its 11th Year of (Extended) LR Warranty / Full LR Service History
(Expensive, but Trouble/Worry free - hopefully?)