British Airways scheduled me on a flight from US with an 45 minute layover in Heathrow. I don't know how the heck they expected me to make the connecting flight

British Airways scheduled me on a flight from US with an 45 minute layover in Heathrow. I don't know how the heck they expected me to make the connecting flight considering I had to go through customs, then security again, and go halfway across the airport. Their system even flagged me as "showed up too late for the flight" the second time I went through security.