Originally Posted by
hhdl
Perhaps OP doesn't have an ETA? That would make them ineligible to enter the UK and then make BA skittish about transporting them to LHR.
Good point, this makes IROPs much more complicated. I wonder whether BA proactively checks for this (or if it's even allowed to query ETA status without directly being linked to the check-in process).
I always used my lack of valid ESTA as the argument why I absolutely can't be rebooked via the US and the airline needs to find something else for me - even though I could easily apply for it, I just want to have a valid reason to avoid accepting such itineraries.