Help please, urgent need to travel and no passport

I am so sorry to hear this. It's the absolute worst thing about the distance.
Safe journey.

Absolutely put any worries of returning out of your head.  If it's a helpful distract, then sure.  If it's not helpful, shut it down. 

You will be allowed in.  I assure you.

And if you want to be slick, just use the e-gates with your USA passport.  No one even needs to know.  Not the "by the book" advice we typically give but as long as you aren't travelling with children under 12, you can use the e-gates. 

I grew up with a strong elderly community around me.  One woman had the exact same birthdate as the queen (month, day, and year).  At 90 she was still playing tennis daily!  And would go kayaking and put her kayak up and down on her car by herself.  She was AMAZING!!! 

And if you want to be slick, just use the e-gates with your USA passport.  No one even needs to know.  Not the "by the book" advice we typically give but as long as you aren't travelling with children under 12, you can use the e-gates. 

The Home Office will know as they used the e-gates with a US passport. The exit checks would also show that visitor didn't leave before 6 months. The exit checks were brought back in to find who wasn't leaving the UK, but it is also valuable data for the Home Office.

The UK records entry and exit into and out of the UK. 

The airlines have to give the UK the names of the passengers on flights: the border officers at ports inform the HO too, as do the UK border officers in Belgium and France. It's how the HO/Embassy staff are able to meet certain passengers as they arrive at the border/try to board a plane to the UK or enter the UK at a port and how the HO prevent certain  people from leaving. It's also how the new law was able to come in last year, to not to have to give notice of removal of British citizenship, so that when the exit list flags a name, they can just remove their citizenship and take their Brtisih passport when they try to enter the UK.

As long as the airline will let you board and you can get to the UK border, the UK border guards cannot stop a British citizen from entering the UK. They might not be happy and there might be a delay.

The Home Office will know as they used the e-gates with a US passport. The exit checks would also show that visitor didn't leave before 6 months. The exit checks were brought back in to find who wasn't leaving the UK, but it is also valuable data for the Home Office.

The UK records entry and exit into and out of the UK. 

The airlines have to give the UK the names of the passengers on flights: the border officers at ports inform the HO too, as do the UK border officers in Belgium and France. It's how the HO/Embassy staff are able to meet certain passengers as they arrive at the border/try to board a plane to the UK or enter the UK at a port and how the HO prevent certain  people from leaving. It's also how the new law was able to come in last year, to not to have to give notice of removal of British citizenship, so that when the exit list flags a name, they can just remove their citizenship and take their Brtisih passport when they try to enter the UK.

As long as the airline will let you board and you can get to the UK border, the UK border guards cannot stop a British citizen from entering the UK. They might not be happy and there might be a delay.

Like I said, “Not by the book advice”.

The OP just lost their mother and wasn’t able to be there.  He/she is definitely a “by the book” person as they’ve looked into what is needed for re-entry.  We all know they will be allowed to re-enter as they ARE British.  I would encourage a bit of compassion versus stating the harshest penalty possible given the circumstance.  I know you have it in you, as you’ve been so kind and supportive during my cancer battle.

Imagine the headline “British citizen stripped of citizenship for using incorrect passport at e-gate”.

Thanks to everyone for their help. I haven't had much sleep due to communicating over the time difference and all the admin and trying to get everything together has been rough. It has however been a distraction until I can be with the family.

I received my emergency passport this morning. Service at the embassy was excellent.

Flight is scheduled for midday tomorrow.

I would encourage a bit of compassion versus stating the harshest penalty possible given the circumstance. 

It was what you posted that I found worrying, which is why I quoted your post in my response.

As already stated here; and has been stated in other threads too;  once at the border they can't refuse entry to a British citizen to their own country. There is no point in arriving at the UK border and then using a US passport to enter the UK a visitor. It's clear the OP is honest.

UPDATE

No problem at immigration on return. Nice lady was very understanding.

My passport arrived before I returned and the photo my wife sent was enough evidence for them although I had about every document and email  regarding my application and citizenship with me just in case.

Thanks again for all your help.

If anyone needs to know how to go into a blind panic in the middle of the night, feel free to ask!