I VERY much doubt they'd allow anything like that amount of tethering.
When I sought a tethering contract [I}the only UK company that allowed it at all [/I]was Three, and that was limited to 2GB/Month which isn't a lot. At the time, 18mths ago, NO ONE ELSE was selling tethering contracts in UK.
They utterly fooled me with the barefaced lie of "all you can eat data" and Tethering allowed". The truth was very different. All you can eat data, sure, but you needed a microscope in the small print to see that tethering was limited to 2GB, and they made very, very certain they never suggested any hint that was the case.
Beware, this is a scamster's small-print heaven, and the mobile companies seem very reluctant to tell it straight.