Thanks for all help so far :
This is an example of how the "extra letter "works
Clue: Conflicts with muscles covering great distances(7). The answer entered in the gridis parsecs - made up of pecs(muscles) covering (W)ars (conflicts) W being the superfluous letter.
12a is entered in the grid as ABE (arab garment) wordplay being AA (carmen) round be(live).
{The Y was from pyjama which can be spelt pAjama}, so thanks for all the help with that one!