I see that three have upped their tethering allowance from 4gb to 12gb. I strongly suspect they were losing punters as 4 gb is a bit tight. A sim only deal of AYCE data, unlimited texts and 600 talk is £25. That is a 12 month contract but you can have 1 month contract if you limit the data to 12gb instead of AYCE.
Also anyone with poor credit will be accepted at www.pgmobile.co.uk. They use the Three network but have different price plans.
"On our All-you-can-eat data plans, you can use up to 12GB of your data each month to create a Personal Hotspot within the UK."