To be fair mate, all i would say is, take a look at this, http://uk.pcpartpicker.com/p/TgcCZL
There is plenty of overclockability on the new pentium for the price. And there is no need to go for an expensive motherboard, i have a cheap Foxconn on mine, and i am running an i7, and GTX780Ti
For a budget improvement build, i would say there is no need to spend over £100, when you can get ample for that. Also, i added a new GPU for you to take a look at, if he wanted a bit of extra leeway