Posters at the Travelex counter proudly proclaim 'double miles on all transactions' so I would have no qualms about arguing all day until I got the miles - pre-ordered or not. Not the T4 staff's fault, but not mine either...

If they want to mislead customers, they're welcome to, but they shouldn't try it on me. I suspect that they're ahead in the long run and they won't lose too much sleep over a hundred quid.

Contrary to others' experience reported in this thread, I was told there was no possible way they could credit the miles, since my receipt showed 0. I don't know if I was being lied to, or LeisureFirst and BahrainLad's tellers knew some magic trick. I will charitably put it down to a computer error.