I don't have a definitive answer, but have been trying to work out the answer myself. The UK Passport Agency will supply a blank stamp free of charge with headings in English and Arabic - with dotted lines in between. Someone has to fill in the dotted line gaps in Arabic. Depending on what you read, this might be done by yourself or a mate who speaks Arabic, or by a translation agency. It won't be done by your own Passport Agency. The Libyan Embassies are supposed to have a list of authorised translators, but they don't. Then, depending on who you read, you are supposed to get the filled in stamp authorised and re-stamped by the translators, or by your own Passport Agency, or not at all. The translation must be stamped in your passport and cannot be on a separate sheet of paper. Again, depending on who you read, the Libyan border guards check that the translation is there but don't actually pay much attention to it once they've seen it's there.

This thread might be useful: http://www.lonelyplanet.com/thorntre...rt=45&tstart=0