I can confirm that mine is unbranded factory unlocked and i flashed the Android 4.4.3 Retail EU to 'return it to stock'. But i only flashed the /system partition. And mine remained unbranded.
mfastboot flash system system.img_sparsechunk.0
mfastboot flash system system.img_sparsechunk.1
mfastboot flash system system.img_sparsechunk.2
mfastboot flash system system.img_sparsechunk.3
So if it is indeed a Tesco version, it may be in another file. Perhaps the boot.img... cant see anything else that would cause it?? Can anyone shed some light.
The other option, as suggested, is that flashing this firmware does not remove Tesco, and it remains that way.
Sony Ericsson K300i --> Sony Ericsson w910i --> Samsung Omnia II GT-I8000 -> SGS1 I9000 --> HTC One X --> SGS4 i9505 --> Motorola G XT1032 --> Motorola G 4G XT1039