Uk user unlocked iPhone 4 tethering not available

Hi chaps, Im sure that before I updated to ver. 4.3.1 I could see the Tethering option in Network .... it aint there now - I have tried deleting the .ipsw files (as advised by wjosten in another thread) Ive reinstalled etc but its still not there ... I have just bought an iPad 2 and was going to mess around with tethering ... probably not going to work cause Im on giffgaff and its against there TACs but thought Id give it a try and if necessary switch providers ... any advice very welcome ... best Roger
1 imac 24" 3.06, 1 x G4 desktop FW 800 and 15" Macbook Pro 2.2 and an iPod Mac OS X (10.6.6) iPhone AppleTV and a little Advent PC as well