This used to be limited to 100GB but is now UNLIMITED!
If you don't want a 24-month contract, then just buy the 12 month SIM only deal which is also £22 per month and put it into a 4G router. You'll get calls and texts also included.
I've heard that the Huawei B612 has excellent performance. The Huawei B525 is available on Amazon so you can try it out and see if it works for you.