I have both e-Rewards in UK and in USA - when in UK, using a UK IP address, if I try to access e-Rewards USA accounts, the surveys wont load.
It would seem that the reverse is also true - if outside of UK, trying to access e-Rewards UK the surveys wont load.
There does seem to be an exception - when in UK, if I get sent to my US account a "QUICK SURVEY" which is worth 25 or 50 points, these surveys will load and will get the points.
So those outside the UK, try and look for QUICK SURVEY should you be given the opportunity - it just may work, and you will get 25 points. That's enough for the 750 Avios reward. Good Luck.
For those in UK - this one was a very simple 1500 points for each family member account.