You have two power options with your phone - a local power adapter that plugs in to the base of the phone (Panasonic KX-A239 or equivalent) or 802.3af / 802.3ah Power over Ethernet. I'm not sure the local power adapter is available in the UK, and it's arguable the messier option anyway - why have two cables going to the phone when you can get away with one?
Any good quality 802.3af or 802.3ah midspan power injector will suffice - that's the beauty of a standard. Any 802.3af compliant source should power any 802.3af compliant sink. How the injector hardware is powered is irrelevant, so long as it is powered correctly. As I said, I prefer the 'one box' injectors, where the mains power supply and the injector hardware itself is in the same box.
There's some cheap Chinese units on eBay - but I'd go for something a little more expensive to protect your fairly expensive phone. TP-LINK is probably the cheapest brand, but you have to be careful - not all their PoE injectors are 802.3af or 802.3ah types, and the reviews on Amazon indicate the quality may be a little suspect.
I pointed out the Solwise unit earlier in this thread, which is from a series rebadged by other brands including HP. If I wanted a single port midspan, that's what I'd buy. Connect the unit to the mains, the unpowered side to your switch (in your router, I presume) and the powered side to the phone. It doesn't matter whether the midspan goes at the router or the phone end - that's the beauty of PoE.
If you intend to buy more 802.3af devices, it may be worth buying an 8 port Gigabit PoE switch rather than a midspan injector.