This may sound a bit left field, particularly from a non-Christian non-child-owning person, but I believe that Methodist Chapel Aid are getting some of the best returns for Child Trust Funds. You don't have to be a teetotal Wesleyan to use them and anyone can open an account with them.
Are they protected in the same way as a bank. We've had a load of grief here with the Presbyterian Mutual Society. When banks started to go belly up people were covered by the government up to a certain amount. As the PMS wasn't actually a bank they weren't covered and when the administrators were called in there was no protection.
I don't know if that's the case with the one you mentioned but it's something to check.