I've recently had my knuckles rapped by the Unit LCE Mafia for not replying "(callsign) correct" after readback by a pilot of an ATC Clearance.
My viewpoint was (and still is) that no such requirement is set out in MATS Part 1, therefore it is verbosity. CAP 413, para 1.13.4 says"ATC route clearances shall always be read backunless otherwise authorised by the appropriate ATS Authority". As the UK CAA, the "appropriate (often incompetent) authority" do not mandate such phraseology in MATS Part 1, they have authorised its non use.
What's next, "(callsign) cleared to land"...."(callsign) cleared to land" ...."(callsign) correct"?