The Ford USA recommendation for most engines is now 5W-20, not 10W-30.
A few vehicles are exceptions to the 5W-20 recommendation, specifically
the SVT (AKA the ST170 in the UK) Focus.  For the exceptions, Ford USA
recommends 5W-30.  There is one vehicle class that uses 10W-30, and that
is FFVs (Flexible Fuel Vehicles).

Source:
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Article No.
     02-1-9 a.. ENGINE - ENGINE OIL - RECOMMENDED APPLICATIONS FOR SAE
5W-20 AND SAE 5W-30 MOTOR OILS - GASOLINE AND FLEXIBLE FUEL VEHICLES ONLY

     Publication Date: JANUARY 14, 2002

ISSUE:
Ford Motor Company now recommends SAE 5W-20 viscosity grade for servicing
most gasoline and flexible fueled vehicles.

ACTION:
All 2001 and 2002 vehicles where SAE 5W-20 is specified should be serviced
at the recommended oil change intervals using SAE 5W-20. This oil is an
improved formulation to improve fuel economy. Testing has validated this
viscosity grade can be used in many previous model year vehicles. It is
recommended ALL vehicles on the following Vehicle Application Listing
be service with SAE 5W-20.

All 2001-2002 vehicles other than those listed in the "Exception 2001
Vehicles" or "Exception 2002 Vehicles" chart are being filled with SAE
5W-20 motor oil at the factory and should also be serviced with SAE
5W-20 oil.

[snip list of vehicles affected]

...

NOTE: FOR 1993 THROUGH 1998 MODEL YEAR FFV USE XO-10W30-FFV.

     NOTE: THE "EXCEPTION 2001-2002 VEHICLES" SHOULD BE SERVICED WITH
     SAE 5W-30 MOTOR OIL.

Exception 2001 Vehicles

     Engine Vehicle
     3.3L  Villager
     3.9L Lincoln LS
     4.0L Ranger, Explorer/Mountaineer, Explorer Sport, and Explorer
     Sport Trac

Exception 2002 Vehicles

     Engine Vehicle
     2.0L HP Zetec SVT Focus
     3.3L Villager
     4.0L Ranger, Explorer/Mountaineer, Explorer Sport, and Explorer
     Sport Trac

     NOTE: IF VEHICLE IS NOT LISTED IN THIS APPLICATION, SAE 5W-30 OIL IS
     RECOMMENDED. REFER TO TSB 99-8-16.

...

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The reason for this recommendation for 5W-20 oil in new Fords is to
achieve higher CAFE (Corporate Average Fuel Economy) ratings.

The reason for the retroactive recommendation in older vehicles appears
to be a condition imposed by the EPA that Ford had to meet in order to
be allowed to specify 5W-20 in new vehicles, to improve the EPA fuel
mileage ratings.

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http://www.ford-trucks.com/dcforum/DCForumID30/524.html refers to it:

     I came across an article that appears to show that the 5w20 weight
     oils are being pushed by the car manufacturers to improve the
     CAFE rating just as many on this board suspected.  After reading
     this letter, I think if I had a 5w20 requirement in my new Ford,
     I wouldn't hesitate to switch to a 5w30! NOtice the emphasis by
     the EPA to make sure that the car manufacturers promoted the new
     oil in order to get the credit.

     http://www.epa.gov/otaq/cert/dearmfr/ccd0112.pdf

------------------------------------------------------------------------
HTH

Mark

5W-30 *is* the recommended viscosity in the UK.

I understood from what US posters here had said, that the recommended
viscosity in the US was 5W-20.

But the climate is different not to mention the differing
environmental/emission standards between the UK and various US states.

5W-30.