UK passport holders are not currently required to obtain a visa prior to travel for either Brazil or Argentina. Your passport must have an “expiry date “ at least 6 months after the date you arrive.
You can visit Brazil and Argentina without a visa for a maximum stay of 90 days.
If you are travelling via the USA You will need to obtain an ESTA visa. This must be applied for at least 7 days before you are due to land in the USA. An ESTA can be applied for directly on the website of the Department of Homeland Security. The fee is payable via a Credit / Debit Card online.
https://esta.cbp.dhs.gov/esta
Peru Requirements
British passport holders are not currently required to obtain a visa in order to travel to Peru. To enter Peru, your passport must have an ‘expiry date’ at least 6 months after the date you arrive.
Further advice should be sought from the applicable tourist authority for other nationalities and for general queries. We strongly advise you to check your destinations' Tourist Board or Embassy for the most up-to-date guidelines regarding passport validity.