Hello Duncan,
Welcome to the forum.
Be advised that this forum is based in the States. As a result, we do not have hands on experience with the Marmitek modules themselves. We do have experience with similar modules distributed here and background on the X10 protocol.
I looked through the TWM4 manual. This is a very capable little device (similar to some of our leviton modules in the states).
The TWM4 is a transmitter only. It cannot be direct wired to a load, and requires a load control (like the LM12) to supply current to load devices. Page 8 of the manual shows the transmitter connected to one mechanical switch (I believe this is what you we referring to). In fact, the device can be connected to up to 4 mechanical switches (momentary contacts or standard) using the Blue (1), Orange (2), Red (3), and Yellow (4) input wires.
The following pdf goes into a bit more detail on the input switch combinations that can be used with the TWM4:
Marmitek TWM4 Folder
Note: The Marmitek web page appears to imply that this device is a RF transmitter - "
* Communication of the transmitters/controllers to the dimmers/switch modules goes via a transceiver. See the complete series of transceivers here"
I believe this is an error. This device appears to communicate through the powerline only (consistent with our transmitter modules in the States). A transceiver should not be required for this device.
Hope this helps. Enjoy,
Boiler