Tether internet with iphone on pay and go o2?

I have an iPhone 4 and I'm on O2 with pay and go where I pay £15 a month to have texts and internet. What I want to do is to be able to tether the internet or set up a Wi-Fi hotspot using my phone. Does anyone know if it is possible to do that with O2 along with the cost of being able to tether?

You might find that tethering is not allowed on most networks, for example giffgaff which is run on the o2 network absolutely forbids it, because if it was so easy to do we would all be doing it, I tried using foxfi when I was with giffgaff but found I was using the data on giffgaff and lost a fiver on pay as you go then noticed their website forbidding tethering probably they want you to spend more money