My theory is that the TCT mystery track may be Money for Nothing.
From the information we have so far-
track is written by MK (from Sam fender interview),
recorded in MK's studio and produced by GF,
very important guitarists are featured - MFN is one of the most famous guitar riffs ever
the involvement of Sting (from Sam Fender interview) who is not a famous guitarist but did sing backing vocals on MFN and so may be recreating these
On a related note, I went to the recent TCT Roger Daltrey show at the Albert Hall as I am a Who fan but was also secretly hoping that the advertised "special guests" may include MK or something related to the mystery project, as Guy did not rule this out on his forum when he was asked (his response was "Still to be decided") but I think part of the reason this did not happen was that there were too many support acts (4) and so RD did not start his set until 10.15 and had to hurry through it to not break the 11pm curfew (the only "special guest" was Kelly Jones who was already there as part of one of the support acts).