Does anyone know what 4E in the sky means?

Bill Knight took this photo in Hemingford Grey

Bill Knight took this photo in Hemingford Grey - Credit: Archant

Bill Knight sent us this photo, which he took from his garden in Hemingford Grey.

“It appeared to be upside down, but I think that it should read 4E. It was perfectly made at a great height with the aircraft hardly visible. The weather was perfect and the writing stayed in shape for some time as there was little wind.

Does anyone have any idea what it was all about?

Bill Knight.