The Welsh computer has a coax output and a resolution of 256x192, can I expect this to display at all on my Philips 50" 4K TV using the same input?
The Dragon 32 has two display outputs. One is a UHF analogue TV signal, which will work if your TV has an analogue-capable tuner. The other is a composite video output on a DIN socket, which you can wire up a cable for with a little effort; most good TVs have a composite video input somewhere.
Both will use PAL-I video timings. These are normally supported by TVs, except possibly if they were sold in the US.