The most common and most likely answer to this crossword clue is the 5 plus 7 letter word PLAIN SAILING
I've seen this crossword clue in The Daily Telegraph
P
L
A
I
N
S
A
I
L
I
N
G
More clues leading to the result PLAIN SAILING
- Not too good east of prairies for a picnic
- Staightforward procedures involving one in poor health
- Midshipman Easy's job?
- Policies about one upsetting a cinch
- Easy progress in scheme to house one son – invalid
- Arrange journey by sea around island – it’s easy
- A breeze travelling behind flier, did you say?
- Intends to circle island in poor health, getting uninterrupted progress
- A piece of cake, means to keep one sick
- Comfortable flats? Well, no
Buddy explains!
The straight part
We know that "uninterrupted progress" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case uninterrupted progress = plain sailing.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.