Complin (more often Compline, but both are in Chambers) is a church service, put in the A from the end of Jura (at last), to get Complain, Rail, rant etc.
Thanks, malone - didn't think to consult the BRB for COMPLIN being a possible word. Not sure of the exactitude of the definition in the clue given the BRB version.
Kenhiggs, thanks again. After your post (wondering about the definition) I looked at Chambers myself. When that wasn't particularly helpful, I consulted Mrs B!