Edit: After half day, my wife’s Mac started having the same problem. I have then applied the solution that I found in the Apple
How To Use Tethering On iPhone For GiffGaff Users Using No Jailbreak
GiffGaff introduced a new price plan a few weeks ago and said that the ?10 sim only contract with unlimited texts and 250 mins 2GB of data would come with the ability to use personal hotspots which was unavailable before but it seemed because Apple did not recognise GiffGaff as a network they would not allow the feature on iPhones but we have got a solution and it does not require you to jailbreak but it does require you to act fast.
FlashArmyKnife just looks like an ordinary app which allows users to adjust the Flash brightness and use the built in calculator but a feature what Apple missed is that the Apple allows tethering if you know what to do. The video up above shows you exactly what to do but incase that was a little fast we have wrote out the command you need to enter in to the calculator to activate tethering , (without comas): 1642, M+, C, 1452, M+, C, 1943, M+.
The app does cost ?1.49 from the app store and can be found here but do not expect it to be around in the app store for long as Apple will remove it once back from the holiday break. This also works on other networks and also on the ?12 GiffGaff plan which includes unlimited data.
UPDATE: FlashArmyKnife has now been taken down from the App store but we have found another solution *Rock Paper Scissors*