They might be going for straight numbers vs quality.
Here's an example:
Navy
UK has 3 combat proven carriers & airwings, 8-12 of the best nuclear attack submarine crews & boats, and a bunch of combat proven frigates & destroyers
Brazil has 1 unproven carrier with an obsolete airwing, only diesel subs, and 2nd hand surface vessels.
Winner --> definitely UK in any blue water and some brown water theatres.
Airforce
UK has Harrier GR.9 & Tornados IDV for bomb trucks & Tornado ADV & Typhoons for air to air combat.
Brazil has mirages which are a full generation behind the Typhoon and F5E's which are a full generation behind the Mirage.
Winner ---> UK
Army
UK troops are significantly more combat experienced than their Brazilian counterparts due to Afghanistan, Iraq, Sierra Leone, Falklands. In addition, the UK has better tanks & AFV's.
Brazil has not had a major conflict of the same scale as Iraq & A-stan. Brazil probably has more troops though.
Winner ---> depends on whether numbers can be brought to bear
Special Forces
UK has SBS, SAS, & Paras
Brazil does not have an SF unit that is at the same level as SAS.
Advantage ---> UK
So... in any conflict that requires Brazil to fight the UK outside of Brazil or South America, the UK will win. Within Brazil, Brazil will obviously have an advantage.
Take these rankings with a grain of salt.
EDIT: Brazil has one of the craziest police forces though. Look up BOPE or watch these vids....
http://www.youtube.com/user/militaryvids. These guys are like military level special forces in a city!