In Oban
Last time I was through LHR T5 was 14 months ago while connecting off an inbound flight from South America only to be told that my connecting flight to MAN had been cancelled due to "operational reasons", but not to worry we were going to be bused up the M6. You do not want to hear what I said about this.
That was both my first BA flight in a number of years and the first time I had used LHR since about 2009. Needless to say my experiance that day and the average to poor BA service on the flight has clouded my judjment re LHR and BA, and I have not returned since to either. T5 is ok but nothing that great, and as others have said the resident carrier (BA) is also no longer what it was, in my admitted now very limited experiance of them.