You havent mentioned how long you will be staying in
Argentina,
Brazil Peru but depending on the length of your stay you will need a visa.
I found the following information on how to apply.
You can apply in a number of ways, for example, by post, by courier, in person and online. Staff at the visa application centres will tell you about the ways in which you can apply.
Some visa sections will only accept applications made online. To find out if you can apply for your visa online please visit the visa4UK website.