not a fup of my own on this particular occasion, but I thought it had been at first... not yet qualified, on my solo QXC, about to take off from a fairly major regional airport in the NW to return to base. Cleared for takeoff on R25, rolling, gathering speed nicely, lift off and start to climb ... and then at about 150' agl I hear in my headset an agitated controller say "Golf Papa Uniform IMMEDIATE RIGHT TURN, I SAY AGAIN IMMEDIATE RIGHT TURN, ACKNOWLEGE" ... the adrenaline kicks in, I scan but can't see anything to conflict and make a rapid turn to the right, climbing out very low over a housing estate. Once I've gathered my nerves, I ask to route to the left as per my original plan, and am cleared to turn with no problem, and handed over to my en route. It puzzled me all the way back to base, where I was signed off for my QXC pass. So I called the tower on the phone and explained that I'd been rather shaken (as an unqualified solo pilot) by the low level turn. The duty controller remembered me - apologised, and said that during a shift change they'd missed the fact that another aircraft was cleared off R28 at the same time. Felt immediately better - I was convinced that I'd taken off without a clearance, even though I'd written it down!