I find the some questions in the UK visitor visa form a bit strange. They ask "How many friends do you have in the UK?", and when I truthfully admit having friends there, they ask me for the friends' personal details like address, phone number and the type of relationship.

This is understandable in the case of the applicant visiting somebody in the UK and staying at their house. Of course the want to know where I wil stay. But why do they need this information about my personal network of friends? And how do they define this word? Do they mean friends like in Facebook, or like a Significant Other? And does entering other people's personal details into a public database without their consent comply with UK law?

Correct me if I am making the wrong assumption...

The visa application form is for the Thai applicants details. If you are completing the application on their behalf, they are not asking about your friends in the UK.

If you say I have x,y and z friends and the last people who also listed them as friend overstayed or they are persons of ill repute then this will go against you,

Indeed, it is the applicant who has to answer that question, who is presumably the boy you refer to here.

What is your nationality? You say that the boy is your son, so if you are not Thai then surely he has your nationality as well and so can obtain a passport from your country; in which case, depending on which country that is, he may not need a visit visa at all.

Obviously, by friends they mean people the applicant knows well. This may include people they only know through social networking sites, but not every Tom, Dick or Harry who has ticked their 'friends' box!