Hi,
TL;DR - No, install a Sonoff Mini4RM behind the ceiling rose and use the existing mechanical switch.
Your diagram doesn’t show a connection to the Neutral terminal on the switch, only two connections to the device phase in (L), and switched relay out (L1).
If you rewired the standard 1mm2 2+E cable to a UK light switch in the ceiling rose to L and N to give a low-current permanent feed, you could connect to L and N on a device to give a WLAN input device.
Realistically, this is no better than a RF battery button (Z-Wave, Zigbee, Thread - £5 from IKEA) mounted over a blanking plate where the switch was. This used to be common with “Smart Bulbs”.
Alternatively, mount a mains dimmer module behind the ceiling rose where L, N, and load terminals are all neatly located. Even better, you can use the standard mechanical switch so no need for a RF button at all.
Get a hole saw a little smaller than the distance between rose screws, and think about the requirement for secondary insulation (I use a custom shroud or a small box in a loft).
On some installs, I’ve used the standard 1mm 2+E to pull in a new 3+E cable from the rose to give a proper permanent live feed and switched load live, but…
Sonoff relays are designed for EU round back boxes (which are explicitly banned under BS7671) so struggle even to fit in a UK 50mm back box. You can buy spacer rings to make the 1G patress stick out of the wall more, but that looks ugly.
There are tens of other posts in here with others struggling with the same issues. The UK has fundamentally different wiring from the EU, different back boxes, and LED lights are very strange loads making no-neutral devices very, VERY unreliable (even with a ballast module).
If this helps, 
this post!
