The most common exams that English language learners take in Britain are IELTS and Cambridge English exams.
IELTS stands for International English Language Testing System and learners get a score, usually between 4 and 8 (9 is the max). Most students take the academic version for entry into British, Australian, Irish, New Zealand, Canadian and a growing number of US academic institutions
Cambridge English exams for adults come at 5 different levels (A2 to C2). The highest exam is Cambridge Proficiency. Not all native speakers (or writers) would be able to pass it!
Each Cambridge exam has 3 pass grades: A, B and C
If you manage to get Cambridge Proficiency, this means your level of spoken and written English is very high.
Getting an IELTS score of 6 or Cambridge FCE (B2) means that your English would just be enough to allow you to survive in an English-speaking office environment. Gaining IELTS 7 or Cambridge CAE would mean you could manage quite well.
TOEFL (Test of English as a Foreign Language) is a US-based exam that tests academic English for entry into American universities.