Redfox
I think you'll find that US controllers save RT time by missing out the words "climb" or "descend". An instruction to climb to FL340 would thus be "BAW123 maintain FL340".
It would also appear that "maintain" when relating to speeds does not necessarily mean "fly at this speed". See the thread entitled "Question for a US controller - 250kts <10".
Maintainingly yours
G W-H