Hi,
it is missing out of the Southen edition as well,i have just emailed the Daily Express so i hope to have an answer shortly as soon as i do i will publish.
Thoughtful of you....however, even if the DE replies, it won't be accepted, as hundreds of people will not be privy to the clue. I think just send it in with 26d blank.
Question 26d has not been printed, it would be wise to submit the crossword leaving 26d open rather than make a guess--Surely Daily Express would accept