when data rates are this similar, especially for cell phones that can't keep up, data caps are the most important. i don't live the uk but any informed consumer would take the cheaper plan and some business would need the more expensive plan.
Is this is 50GB/month - who uses 50 GB/month on a cell phone? - I am a business user and rarely exceed 500 MB even with people sending large powerpoint presentations around. . . . . mind you the smart smartphone users have their smartphones connected to Wi-Fi in the office and at home which helps keep data usage down, still the plans in the UK look cheap compared to what we are paying in Canada.