I've come to a grinding halt with my final three. :s
Most hinges on 25a, which despite the helpful previous posts I am being very slow in grasping, if it's the answer I think it is (a loose synonym for "most panicked", also the title of a Godard film... but I still can't understand the parsing, or how precisely the wordplay relates to the driver alcohol test that the rest of the clue seems to point to...); then that leaves me with L---L-L on 18 down which I'm also at a loss on.
Finally 20a seems to be a reverse cryptic referring back to 19 across but there doesn't seem to me much to go on beyond that?
Thank you forum!