Just online at Farnborough, delighted to see Jerry on the apron as I logged on. Flightplan to EGNS (home). Winds calm, he was heading for runway 06. He called up. Herein I have to apologise, my performance was poor, I suggested a heading from 06 which should have routed him direct to NORRY, his first waypoint. Traffic was light but mostly using 27 at Heathrow. Diamond 068 took off and turned on a heading which kept him out of EGLL airspace but on a Northerly heading. I should have asked, but as I didn't confirm any clearance, I watched as he climbed, still Northbound for another 10 miles, at which point I wondered if my 300 degrees had been heard as 360 degrees and asked. Jerry accepted "own navigation" and spent some time travelling West to regain his original flightplan......Sorry. This only serves to highlight the need for clearance so that both parties are aware and can follow the flight progress. I'm still trying to avoid the pregnant pauses over clearances as I look up the lesser used ISEC's and Fix's... Once again apologies offered. G'day