I have eaten a handful of times at Chez Gerrard in the international departure lounge at Heathrow. I have always found it to be reasonably good and reliable. They claim the prices there are no higher than what they charge at their nearest restaurant outside of the airport.
Yesterday, my wife & I had a mid-morning layover of several hours at Heathrow. We headed for Chez Gerrard for breakfast. I had "L'Anglais," the basic British morning fry-up. It was 6.95 pounds. I thought it was quite good and the portions were quite ample. It includes 2 eggs (fried or scrambled), 2 bacon slices, 2 sausages, roasted tomato & mushroom, baked beans (served in a small ramekin) and a couple slices of baguette. I had the scrambled eggs and they were cooked perfectly for my taste. I believe they serve this all thru the way.