Just checked out the sim only deals linked in this thread, and they all state tethering is not permitted.
What i wanna know is, unless your up to no good downloading loads of illegal stuff via bit torrents, how are they going to know your tethering? The only way I can see is from the content and quantity of downloaded files. If your just a regular web user doing everything above board, how will they know if your browsing on a phone or a laptop tethered to the phone?
Ive just used over 8gb with my laptop tethered to my giff gaff sim last month. and have just paid for another month and they told me how much ive used, no problems. 3 have the only sim card that has tethering allowed, its called the one tarrif. the 3 one sim is £25 month unlimited tethering and 5000 texts and 2000 mins on a rolling one month contract,