....... had a play last night and it worked fine , going away for the weekend and want to use this arrangement for browsing the internet , surely this is only going to be the same for data usage as if i was using the phone to browse the internet , or am i missing something

Terms and conditions maybe

and that means what ? , if i do 500mb / month through the phone or 500mb / month tethered what difference does it make

It's ok, it will make no difference.

I tether all the time, never been pulled up on it. Just stay with your allowance to not bring attention or big bills to yourself.