Peter
I just checked the tracks recorded on my GPS.
Between 1441 and 1452 on the day in question I flew between Haslingdon and Hoghton routing more or less along the M65 in my 29 year old 4 cylinder 3 blade silver and blue Enstrom F28A G-BDKD. 2200 ft over Haslingdon descending to 1250 ft over Pleasington. I was happily pottering along at 50-60 MPH.
Its been called some things but never a flying shed before.
Cheeky sod!
The silver bits are hard to see against a grey sky which could give the impression of a high tail boom.
Ill see if I can post a picture of it.
Try this
Enstrom F-28A
or this
and if you're interested, a picture of it when new