£51 for 5GB of data is expensive. I'm in the UK and on t-mobile I pay £17 per month for unlimited data (not 4G though), all calls and all texts (well there are limits, but for my moderate/heavy usage it's as good as unlimited) and those calls include some international.

And until this year, it also included a free handset, last one 20 months ago was a desire HD. So £10/GB does sound expensive.