picture would help. How old is this plant? Is it flowering?
Are there peppers on it yet?....

I 2nd the pic would help.

What type of pepper is it. Chinese (Habanero etc.) tend to exhibit "crinkly" leafs now and then with no ill effect.

Too much fertilzer. Cut back and water only. You may get lucky and the next sets of leafs will be normal.

Not sure which it is , either jalapeño or habenero probably (and hoping) the latter.

It was part of a batch of random chilli seeds I'd saved from chillies I'd eaten.

http://www.flickr.com/photos/22085785@N07/4898099851

It's defiantly not the fert as it's always been like this from being a small plant and it's been repotted along with others, unless o course this plant is my only Hab and they're particularly sensitive to fert

Looks like overwatering to me. Also that soil looks very dense. You could either cut back on the watering schedule or preferably add about 20-30% perilite to that soil and repot in addition to cutting back the waterings.