The Japanese mains voltage is 100 V, 50 or 60 Hz (depending on the region).
The US mains voltage is 110 V, 60 Hz.
The UK’s is 230 V, 50 Hz.
The frequency should not matter for consoles. As far as I am informed, all consoles sold in Japan we sold with the same PSU regardless of whether they were sold in West Japan (60 Hz) or North/East Japan (50 Hz). The voltage does matter.
If you are looking for a one-size-fits-all device, you need a step-down transformer that will take 230 V and transform it down to 110 V. (The difference between the Japanese and US voltages are small enough to be within tolerance; transformers aimed at making US products usable are more frequent.) The consoles don’t need much power so your average low-end transformer will do the job. Here is a link to a sample from amazon.co.uk. Note that I am not specifically recommending this model over any other model, just pointing out one that will work.
For every console there is also an option of powering it with either the first-party local PSU or a third-party local power supply. However, each console is different and you want a general one-size-fits-all. (For example, the EU N64 PSU can be used to power a JP N64 in Europe but the EU SNES PSU should not be used to power the Japanese SFC equivalent as the former outputs AC while the latter gives DC.)
The TV thing is easier. Most European CRTs from somewhere in the mid 90’s were able to display the Japanese/US NTSC standard. As you get to CRTs that were produced towards the very end of the CRT era, you can pretty much assume they can cope with NTSC signals. The console video signal will typically be supplied with composite connecters (yellow/red/white RCA connectors); just plug this into the TV. If the TV only has a SCART socket, use an adaptor. This will serve you a picture in an acceptable quality.
For some consoles, acquiring an RGB cable for better picture quality is really easy since they output RGB natively (e.g. SNES/SFC). There are even more European TVs that can take RGB than those that can take NTSC. RGB is usually supplied with Scart cables.
If you happen to be really unlucky and have a TV that can only display PAL colour (the European standard except for France), the picture will still be there but in greyscale.
Furthermore, most modern flat-screen TVs will also accept a composite cable and will likely be capable of displaying the NTSC signal. However, lag may be an issue.
So to sum up:
- Simple step-down converter from 230 V to 110 V for the console
- A UK CRT TV as a TV set.