British nationals do not require a visa to visit Bolivia for 30 days. This can be extended for a further 60 days at no extra cost, as long as you apply before the end of the initial 30 days. You can apply for this extension at one of Department of Immigration offices. Ensure that you receive an entry stamp on arrival, otherwise you will have to pay a fine to leave.
Your passport must be valid for a minimum period of six months from the date of entry into Bolivia.