Visiting students or trainees from Bolivia are exempt from UK tax on payments from abroad for the purposes of their maintenance, education or training (Article 20(1)).
Also, a visiting student or trainee’s earnings from activities exercised in the UK are exempt from tax provided that they do not exceed £3,500 plus the appropriate level of personal allowances (Article 20(2)). The benefit of this latter provision is only available for up to five fiscal years.
See Article 20 for details and also the guidance at DT1930 - DT1931. Refer any case of difficulty to Employment Income, Technical.