Battery powered security lights..??

[flameport]

Either get a separate PIR like this: http://www.toolstation.com/shop/p56072 and a short piece of wire to connect it to the existing light.

Or get a light with a PIR built in like this: http://www.toolstation.com/shop/p11271 to replace the existing light.

Either way a 10 minute job to fit, existing wiring can be used, no need to cut holes in walls or anything else.

 

[SimonH2]

What would the wiring there entail?

Fairly simple. Needs a short length of 4 core cable (3 core + CPC).
Neutral & Earth are connected to the same terminals as the light is already connected to. The Live feed to the light is disconnected from the fitting and joined to the cable going to the PIR (needs an extra terminal). The 4th core is used to bring the switched live back from the PIR and is connected to the L terminal on the light fitting.

Note that there are a few PIRs which don't need a neutral. Avoid these - they will only work properly with incandescent lights.