Cheers for that, the physio I go to actively wants me to go to a specialist in the area and get a scan / x ray or whatever to make sure there's nothing untoward happening in there. He also advises me not to sit for too long.
As I said the back isn't to bad now (TBH I've had quite a few bad backs but nothing with referred pain down the leg) but I certainly don't want it to happen again.
I'm 27 so hopefully this can be sorted out.