I am intrested in putting some sort of switch over the current switches to stop some members pressing them, what ones will cover a UK switch? 
I don’t know of any which fit UK shaped switches. What I think most community members do is just put a small box case over the existing switch and then mount a battery operated switch on top of that.
For example, the Aeon wallmote is the right shape for this, but there are quite a few others to consider.
(Again, you have to make your own box cover, then you just put the battery operated device on top of that.)
You can see other battery operated devices in the buttons FAQ. This includes both battery and Main‘s power devices as well as ones for different geographical regions, so read the descriptions carefully to make sure it matches what you were looking for.
The FAQ is intended to have only one or two posts per device and should include a link to a discussion thread where you can take follow on questions. Otherwise, come back to this thread and ask any additional questions you have. That way the FAQ stays easy to use. 
FAQ: Full list of buttons and remotes confirmed to work with SmartThings
There are also quite a few ready-made options to use with the Hue dimmer switch, but there’s no official direct integration for that device with SmartThings. If you are also using a Hue bridge and the only lights you are concerned about are lamps connected to that bridge, then that’s another option.
Here is just one example:
I got the dimmers working but it is a bit of a hack and it’s not 100% reliable so if I were you I’d stay away from the hue option (unless you’ve got a bridge) or you enjoy hacking code 
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Have you considered swapping switches out for ‘fish key switches’? The ones they use for emergency light tests where you have to put a ‘fish key’ through a little slot to change the switch. Still means you can toggle the switch when required but you have to work at it.