While travelling to the UK (UK passport holder) my passport was lost. I travel back to the US on Saturday and I'm a green card holder.
Looking at prior questions ( UK to USA with Green Card and without passport) it seems legal to travel to the US with only a green card. The OP on that question was able to check with Gatwick ground services and get an email confirmation.
Would anyone have the contact details of the team in Heathrow that would be responsible for checking passport exemption status?