Bit confused with this light switch, I was expecting more wires, but instead I've only got two 
Black L, brown N, so I can get the Shelly to power up OK.
I can also get the Shelly to recognise the switch input, as wired in the attached photo.
I'm having a mental struggle trying to figure out how to close the loop with the relay (so that the lights work).
Thanks, D
Hi and welcome to the forum.
Shelly1L should be used, Unfortunately currently not available.
Your installation is missing N at the switch. 
Indeed - in this case you’ll need a Shelly 1L, and possibly a bypass. You should wire the Shelly 1L according the following diagram:
Please forget the second switch shown in the diagram! Connect pin L of your switch to pin Sx of Shelly 1L and the arrow pin with pin SW1 of Shelly. If your bulb has a wattage of less than 20W, you’ll need an bypass too.
Addendum: Sorry - was too slow (or have used too many letters). 66er reached the goal at first…
Update ... possibly figured it out ... install the Shelly here, instead of at the switch. The two wires from the switch connect to L and SW on the Shelly, then figure out the rest
