Need to buy a Mac mini (2014) AC power cable (2 prong), urgently.

The current and for the last few years Mac mini computers have used a type of power connector officially called a C7 but more commonly referred to as a 'figure of eight'. This is a completely standard cable and is not special to Apple or the Mac mini.

See http://www.amazon.co.uk/White-Figure-Mains-Power-2-5Amp/dp/B00DT4LRQK/

While the above would be mail-order from Amazon most electrical stores will sell this type of cable including Maplin.

See http://www.maplin.co.uk/p/2m-power-lead-with-figure-of-8-connector-white-n46da

Note: I chose the above Amazon one as an example because it is the same white colour as the original one Apple provided with the Mac mini. Most stores will probably only have it in black but that will of course work just as well.

As John says these figure of 8 cables are extremely easy to get, they are available from ASDA, Currys, PC World, B&Q, Homebase and any high street shop that sells electrical items.

yeah both my non dvd old cd player and my sony playstation2 use the exact cable

The times I had needed to use a third-party power cable with a Mac mini it has been finding one in a box of spare cables that all IT professionals build up over time. I therefore have no idea what make or part number it might be and suspect it is one from old product e.g. old external hard disk power supply.

Yes they might need a generous push in to the socket but my experience is that they do fit.

As you have seen other comments here had tended to agree on this being a standard socket with nothing special needed.

Have a look at this on Wikipedia - https://en.wikipedia.org/wiki/IEC_60320#C7.2FC8_coupler

Compare the picture to your Mac and cable. I can see that in the above the example cable has 'shoulders' whereas the cables I have used have not, the shoulders might make it harder to fit. The examples I gave you previously did not have such shoulders.

It seems that the figure of eight/C7 IS actually different to the Apple supplied power cord

No it is not

the man at Maplins may have been correct after all.

No he was not

I've pushed it pretty hard, but something stops it from going in.

Either the pins in the connector of the Mac are damaged, the socket connector on the cable is damaged or you have not been able to fit the connection correctly, there is a deliberate amount of resistance when connecting to prevent disconnection.

Go into the nearest electrical store with your MacMini and try plugging in a few fig 8 cables, the first one that fits properly, buy it.

Im replying using the MacMini, powered and connected from a fig 8 cable bought from Asda.