Noeyedea to get the answer to 18a look carefully at the words that follow "leaderless" then make them so, and the answer should leap out at you! It was my LOI so I had something of a PDM then kicked myself...
I'm flabbergasted that there are people saying they found this to be on the easy side, even after I worked out how 13a worked it took me an age, especially as I'd never heard of 6a, 19d or 25a, and needed the crossers & Google to resolve them.
A very good crossword though, worthy of a prize indeed! Thanks to Brendan(s).