Check out Amazon UK - I've been happy with APC at work and home. This unit may be a good fit for your use - it is similar to the one I have for my home server, cable modem, and WiFi router - I like the hot swap battery feature. The previous APC unit had replacable battery cells but it had to be taken half way apart to get to the batteries.
Mine came with a USB cable that plugs the battery into the computer and it is compatible with the Mac energy saver control panel. I set the computer to shut itself off after 5 minutes and tested that it worked. It did. When the power flickers (as if does here in rural USA) my server doesn't miss a beat.
Shutting down: when the UPS is connected to the computer and you configure the energy saver for shutdown the computer attempts a controlled shutdown. Not all programs are well behaved all the time though. I generally don't walk away from my computer with unsaved data (that should be everyone's habit) so it isn't an issue for me.
How much time: that depends on how much power your devices draw and how big UPS is. APC has a configuration helper on its web site to help you decide which is best for you. In my case, I know if power is out for 5 minutes it is likely to be out more than 20 minutes and what I deal with mostly is a nearly weekly flicker outage - just enough that the computer goes off. At work we take a different approach and went with BIG devices that power core services for up to 90 minutes. You don't want to know how expensive that is
The thing for me will not be that I am away, it will be that I am working and I lose everything because the power's gone. I am more looking for a solution that allows me to manually shut everything down, keeping the state in memmory, as OSs from Lion and beyond allow for.
I was wondering, as Desktops are generally left on, but in sleep mode, it will be that time that I need the shut down operation to take over, can that be configured for?
I tried the wizard on the website, but it advertised a slightly different model: the "APC Power-Saving Back-UPS Pro 900, 230V", however I couldn't feed it the exact data I wanted to, it didn't have all of the options, I'll have to ask them, but it's a fairly easy setup.
The model quoted me a 17minute run time, what of the model you quoted me, how much do you think (off of the top of your head) do you think I'd get with that. It would be a Mac Mini (two internal HDDs: one SSD, the other a traditional HHD, but I know not the RPM), 27@ cinema display and that's about it, possibly a tethered LaCie 2big 8TB external HDD, but it would happen right then wouldn't it.
Power London is prettey good, it would only be if someone was using the cooker and flicked the switch, or something like a street outage (which has happened, but I had a MacBook then).
Have you ever set the energy saver of your mini to do a scheduled shut down? When you set that up, if the computer is asleep when the scheduled shutdown time is reached the computer wakes up and then shuts itself down. The UPS is going to work the same way after you configure the energy saver for UPS mode. The Mac doesn't need special software, it uses the energy saver control panel.
Your mini should be drawing around 90 watts. What is the display and external drive rated at? I know my kit draws just over 200 watts so theoretically my UPS will give me a bit more than 10 minutes of power. I do a bimonthly test and that's just about what the energy saver shows as well. Add up the total wattage of your kit. The APC site should have a graph for each model showing its up-time for wattage drawn so you can compare models to your wattage.
Remember, the longer the device needs to power your kit the more expensive it is. If all you really want to do is experience a controled shutdown when the power goes out you don't need a big UPS. On the other hand, if you want to continue working for x number of minutes (or hours) while the power is out then you need the bigger model. Only buy as much as you need but also don't buy too little. Clear as mud, right?