How can I unlock tuning function on my Thorn TV P1482T?

The programmes currently tuned in have been inadvertly 'locked' using the buttons on the TV itself as I do not have the remote control for this model. In this situation I cannot retune to the frequencies that I need. Can anybody advise me how to unlock the tuning function using the six buttons on the TV? I have tried all buttons individually and in pairs without success.