According to a reply given in the Parliament by Minister V.K.Singh, there are thousands of Indians languishing in foreign jails. The maximum is in the gulf countries with 4,615 in Saudi Arabia and 6,653 in UAE. In United Kingdom there are 1,467 and Singapore 450. The data covers for the period 2012 to 2015.
The charge in most of the cases seems to be the violation national frontier rules of these countries, which mean that the Indians have been imprisoned for trespassed entry with out valid documents.