programmatically controlling power sockets in the UK

There is really no differences on what you have to do on the US and on the UK. What you need is either use the parallel port, from which you can control 8 sockets without hardware multiplexing, and up to 256 with multiplexing, or a microcontroller with serial/USB communication support (you could use PIC, which are easy to program with assembler) to control the same kind of hardware: a board with either triacs of relays (I'd recommend relays, as with them you don't have to worry what device you connect/control) that support the voltage of your electric grid, and some transistors to actuate the triacs/relays, to decouple the control circuit with the power circuit.

The DIY hardware needed to do this is not really that hard, and you might learn some if you've never done electronics.

If you have a computer with a parallel port and a small amount of devices to control, I'd go with a simple circuit that couples every output of the port to a transistor that actuates the relay, which closes the circuit for each device.

There are some already built circuit boards on the market that you can buy, but I can't overstate the fact that it's not hard to DIY.

_{(source: electronickits.com)}

There are X10 products for the UK (and European) power systems as well, complete with UK 3-pin plugs.

The projects you've seen for the American system can be applied to the UK simply by buying the UK version of the products.

To send and receive commands on the powerline, you would need the CM12 module, which can be programmed through the serial port as you require. In addition there is already a selection of off-the-shelf software that can control the CM12 module. It might be easier for you to interface with such software, instead of controlling the CM12 directly.

A popular online vendor of UK-based X10 products is Let's Automate.