I get somewhat weary of these stories - poor little British innocent abroad ends up in jail facing some awful punishment whilst being held in terrible conditions prior to being put through some quasi-mediaeval show trial.
The parents at home wail about their sweet, loving and trusting son/ daughter who would never ever commit such an offence whilst the press either bang on about how outrageous it is that a British national be subjected to such barbarity and how we must bring them home forthwith for a fair British trial(right wing) or whimpers about human rights and wheels out rent-a-quotes from Liberty and Reprieve (left wing).
Unfortunately, in the vast majority of these situations it turns out that the person is guilty of the offence they're being charged with and, guess what, is therefore subject to the laws, prison and trial procedures of that country. Exactly the same as if a foreign national commits an offence over here. It seems somewhat unclear to me (to say the least) why being British should be some sort of mitigating point.
If, let's say, an Lilliputian national in Britain said "but back in Lilliput, we are never sent to prison for armed robbery, your laws are strange and barbaric", the British judiciary certainly wouldn't say "oohh, sorry, you're Lilliputian, I hadn't realised, just tootle off then and don't do it again". We, on the other hand, seem to have some concept that our citizens can sit outside other countries' judicial and penal systems if we don't really like them.
Well, except the US of course, where the government would extradite our kids to face the death penalty if they asked.