The MacPro 2012 is discontinued worldwide and has been since 2013. You can find secondhand ones in the UK on eBay.
It is worth bearing in mind that you could also buy a 2010 model Mac Pro and upgrade the CPU processors to make it fully equivalent to a 2012 model - I did this myself and now have a 12 core system.
The power supply is universal and auto sensing so all you need is a plug adapter or new power cable.
A final thing to consider is that the Mac Pro is a very heavy computer so the cost of shipping from the US to the UK might be quite significant.