I make about six trips to London a year, and this is the first and only time this has happened to me (last year).

I was going through Immigration and after answering the usual questions I was asked to show my return ticket. Return ticket? Who has those now? I explained that it was an electronic ticket so I have no physical ticket. He then asked if I had any proof that I had a return ticket. Not used to printing any kind of receipt or itinerary, I told him that I do not. He then intimated that he could refuse me entry (intimated, as it wasn't a "threat").

I explained to him that I was not a student or homeless person, but a middle-aged businessman who had no intention of permanently staying in the UK.

After a little more back-and-forth, he "allowed" me to enter.

I now take a copy of my itinerary and receipt with me when I travel overseas.

As to the hotel question, I know I was asked for a receipt leaving a non-US airport once, but I can't remember where that was. I don't think it was LHR, but it may have been a European one.