Upvote:1
The UK is not part of the Schengen zone. As a Brazilian for tourism purposes you can get 6 months to visit the UK without a visa. You also do not need a Schengen visa to travel within the Schengen zone. Some European countries are not part of the Schengen zone.
Every time you enter the UK it is counted as a separate visit with a new 6 month allowed stay stamp on your passport. You can only stay within the Schengen zone for 90 days in a 180 period, regardless of leaving and entering again.
You are never entitled to have access to any country, the border country (UKBA in the UK's case) will ask you questions and assess the purpose of your visit and whether to let you in or not.
Generally as a rule of thumb it would be wise to bring onward travel and proof of accommodation. Also bringing proof of funds would be useful. The UK border is a tough one, so to be safe bring extra documentation.