Hi!
This is my very doubtful version which more a guess, than something serious.
Could it be, that the company Herrtage, Holyoake and Co. presented only their products - "web nuts" - at Olympia show? "Eric" could have been just a set of drawings to demonstrate application of these tech components they made at the time. Really, if the company has never made any car, why it should be on some encyclopedia? Why its "Eric" is in two foreign magazines but not on any British magazines which would of course, I think, describe their car in at least some sentences. As we see British sources tell us only about products, not cars.
So, to sum up, I have doubts that this Eric cyclecar was ever made in any physical form. Otherwise, if it really was, it would be a strange phantom car completely missed in the history of cyclecars.