But where did the name come from? A common misconception - maintained by Morland's and now Greene King as well as this Wikipedia page - is that it is named after an old MG saloon used by the factory for running around and odd jobs, which was kept outside the paint shop and got splattered with paint, which gave rise to it being called the "Owd speckl'd un" (or other variations depending on what you read). However this Wikipedia page on Morland's says it was taken from a car "... called the MG Featherweight Fabric Saloon made from cellulosed fabric stretched over a wooden frame and was black speckled with gold.". Proof if any were needed that anything you read in Wikipedia needs to be taken with a healthy pinch of salt until you can verify it elsewhere.
If you read the Greene King history page you will see portrayed an MG 14/40 with the registration WL3450, and the 'paint splatter' origin. The car body has been tinted in red, but you can clearly see a speckled finish. However far from paint splatters, which would have been irregular and everywhere, the mottling is far too regular and consistent. It also begs the question of just how haphazard the paint spraying was, if operations inside could splatter a car parked outside!
In April 2003 in the newsletter of the Twin Tiers Sports Car Club Ian Parsons recounted how the car that the beer Old Speckled Hen was named after had been in his family since the 40s. He summarises the early history of the car as being "detailed in Robin Barraclough and Phil Jenning’s book "Oxford to Abingdon" being identified as the first ever original production MG called a 14/40 featherweight based on a Morris 14/28. The name "featherweight" was gained as a result of the optional specially designed lightened body to improve the power to weight ratio. As the first original MG it also featured in the September 1927 Autocar magazine and when MG had their first ever Motor show appearance in 1927 the 14/40 on the stand had the same registration number WL 3450. Apparently though history records that these plates were just borrowed for the show car and the actual WL 3450 was not shown. The factory kept the car for a year as a demonstrator/prototype and various developments were carried out over this period. The registration number is credited to the car known in the factory as "The Old Speckled Hen" due to Cecil Kimber's enthusiastic attempts to create an alternative and different paint scheme which included a speckled body." This clearly indicates the speckling was deliberate.
Verification of this deliberate paint scheme and hence (I maintain) the true origin of the name of the beer, is contained in 'MG by McComb'. F. Wilson McComb describes (p58/59) how a lightweight version of the 14/40 was produced with some peculiar colour schemes - "one of the strangest being 'grained black fabric sprinkled with gold dust' - which at Edmund Road earned that particular demonstrator the name 'Old Speckly Hen'".