Do you mean the PLUTO line at Boulogne? Or do you mean the short lines from tankers going into Port-en-Bessin?
Tom, I wasn't being specific at all....which was exactly the point; the lack of specificity - how many
drivers would know what was coming out of the pump had changed?
Why in heaven's name would the British War Office change the octane level of the fuel?
Becuase they
could???

"Pool" was truly awful stuff, even the military grades;
civilian "Pool" was amazingly bad, scarely more combustible than parafin. Take a look at THIS
http://news.google.com/newspapers?nid=2 ... 43,6562315 for some of the difficulties with it. The quality of "Pool" actually plummeted
again AFTER the war -
http://hansard.millbanksystems.com/comm ... ool-petrol
To cut a remarkably technical story short - "raw" petrol has (had!) a range of anti-knock agents -
but at THAT time principally tetra-ethyl lead 
(Ah, the good old days! I can still SMELL it in my nostrils!) - added to bring it up to a tested octane rating. It's a complicated and expensive process when reckoned in millions of gallons a year...and required the supply of a whole range of strategically-vital chemicals ensured....or the
finished product bought direct from the U.S.
Now - add something to a given amount of petrol to increase one particular property of it....and it's
diluted, basically it is made less volatile by %per volume of what's been added! So THEN various extra volatiles were added to ensure it BOTH hada high octane rating AND went bang!

Obviously - this is what you want
But if you DON'T add anti-knock agents, or rather the absolute minimum

you don't have to add extra volatiles...but it
ALSO means that the petrol in your tank isn't quite as inflammable as the high-octane stuff with it's added volatiles.
Ever tried lighting a small amount of Unleaded with a naked flame? (SAFELY
) You'll find it's VERY poxy stuff to actually make burn!
Now - if you can alter the carburetor settings and ignition timing to suit in a given engine...it allows you to run high compression pistons and thus get more power, because the the lead anti-knock agent stops PRE-detonation....or the mixture going bang under compression WITHOUT a spark...
...like DIESEL engines do
But it means that engines running with the ignition retarded to handle low-octane fuel - DON'T MAKE AS MUCH POWER AS THEY OTHERWISE WOULD.
BUT....if you have an engine
DESIGNED to run it's
best on
low-octane fuel...and you can't alter all the settings to compensate for when "hi-test" fuel is used - said engine will experience problems
because of the higher temperature of combustion in the combustion chamber -
hi-octane fuel ONLY gets you more power in an engine DESIGNED for hi-octane fuel 
Remember how in Ye Goode Olde Days, engines designed to run on Four-Star would run poorly on Two-Star? (Regular vs. Premium for American readers!)
Now....the thing to remember is - that in even just the British Army alone, ALL its vehicles lumped together were running
DOZENS of different types of engines -
but the majority of them were still holdovers from the late 1930's MANY types of vehicles were running tuned versions of pre-war "civilian" motors had been overtuned for performance or strengthened for reliability....
then DE-tuned to run on "Pool"! For instance - you only need to look at the history of British
TANK design to see THREE main streams...
1/ a range of designs using various existing bus or lorry engines cobbled together in various ways
2/ a range of
over-tuned versions of the Liberty that needed a decent octane rating to ensure they could handle the extra power teased out of them without "pinking"!
3/ The Meteor family when it arrived - a
DE-tuned....but still powerful! version of the Merlin!!!
To the British - the chance to raise the octane level of "Pool"
and thus get full power out of a whole range of their vehicles ....while at the
same time starting to reduce the maintenance issues they had from
using "Pool"...would have made perfect sense. With the winning of the Battle of the Atlantic mid-war, supplies of hi-octane fuel from the States was virtually assured, the supply of British-"owned" POLs coming from holdings in Venezuela was assured (we actually got more from
there than the U.S. during the war

It's why Aruba etc. was so valuable....and why u-boats shelling it was so dangerous!)
we had assured supplies of everything we needed to improve "Pool" petrol....why NOT do so???

Twenty years ago we had Johnny Cash, Bob Hope and Steve Jobs. Now we have no Cash, no Hope and no Jobs....
Lord, please keep Kevin Bacon alive...