So there is absolutely nothing stopping a Chinese carrier flying to MAN if
they really wanted too then, since 2007
In theory, not that I know of.
Like I say, Air China have held the rights to 7 weekly MAN-PEK flights since 2007, and according to the CAAC request, they intended to use them from 2009 onwards.
The UK side could be the only issue. There are currently 4 'unused' slots, but that is not to say another carrier has already got those slots but not yet using them.