Have a look at this site . I use them for just the Sim card as I have a sim free phone. I know nothing about there internet service but it look's quite good and may fit your bill.
BTW where are you on the cut? I've just been offered a free 2 week cruise from Oxford to Castleford at the end of September. The owner wants his boat taken home after being on hire during the summer. He say's 250 miles and 90 locks which I reckon to be 85 hours cruising. Is that a holiday?