The guidance is available in CAP 413 section 4 Aerodrome Phraseology, it stresses " take off clearance" shall be issued separately from any other instruction, it follows, therefore, that you cannot accept a line up and take off at the same time. "ready for departure" is the correct phraseology, it assumes you are just that, i.e will not be doing engine run ups or checks on the runway and can accept a " take off" clearance. This is our bread and butter stuff guys, know it, know where to find it and keep the standards high.