In My Account, under 'Control Your Bill', I find I am unable to select an alternative Monthly Allowance from the one currently selected. None of the alternative allowance amounts allow themselves to be selected.
OS: Windows 7 Home Premium / Browser: Google Chrome (both fully up to date).
Solved! Jump to the Best Answer.
Click on the text not the radio button. Yes, I know it's not intuitive... but that's developers for you!
Click on the text to the right of the radio button and the button will change to green. It does for me.
Let me know if that works for you and if not I'll escalate a fault report.