I am very, very sorry to hear your problem.
As a side note, Warranty is primarily an insurance product. There are state (not Fedderal or International)) laws concerning the evaluation, payment and subrogation of claims in the USA.
Certain third parties while very competent, may not fall into the guidelines set by the Company in being the "adjuster" or claim processor.
While this is not going to be what you want to hear, many companies will deny a claim altogether unless the correct notification, assesment, sequence, and third parties are included.
In essence they have contracted already with dealers, technicians, insurance companies, lawyers, and other thrid parties to handle such events (ie, Labor rates, repair hours, parts discounts). The reason here is their "underwriter or re-insurance company" will not pay "exception" claims because of such events, so they would dip into their own warranty accruals which I would imagine are for catastrophic loss events or product liability (Car flips, explosions, deaths).
Another issue, is precedent. Once Ford starts honoring thrid party warranty work, then everyone wants to take their Focus to that 'best' 3rd party.
Also, the Parent liability chain is at risk; warranty claims are in many instances recalls or defects, so the Parent ownership, gurantee, liability shields/limits can be pierced if a non-affiliated/indemnified party performs work that is later subgect of cause in catastrophic or systematic failures.
Not having any work done; waiting to ship the car back to the USA or Ford UK dealer; and waiting for an authorized Ford dealer to complete the work is probably their protocal.
Having said that, most companies will seek a "settlement" (15-50%) of the loss with you, because in essence you have not assisted them in good-faith in this claims process. Thats essentially the insuance/warranty language that is part of your "duties". Its buried in the standard customer warranty/product liability fine print.
While your frustration level may ease, knowing this is essentially bureaucratic rules against your situtaion v. Ford being uncooperative.
At this point, its really fine print minutia of where liability stands, which is a question for Lawyers not Engineers/Mechanical Experts. The net-cost of pursuing this $12,000 would make that not attractive.
I would push for an extension on your warranty for 1yr or loss of usage. Thats a "soft dollar" amount that can be negotiated.
Good Luck for speedy resolution.
Classic/Exotic Car frustation has to be the 10th circle of hell.