Slimline 16A keyswitch. 

We have sold 1000s of these over the last decade or so, and never had a single return - so we class these as just about as reliable as you can get ! 

Electrical insert is the microswitch push-button type, which means that the keyswitch can be easily modified to use as a one-way switch just be taking out one of the microswitches from the enclosure. 

All of our keyswitches have a security plate so that the switch cannot be opened without a key.