Entering a big country like the United Kingdom requires a Visa. Some countries can be entered illegally quite easily. However, don’t ever think to enter UK and USA without the legal Visa. The consequences can be very severe, and you’ll likely get permanently banned to enter those two countries. As for the UK visa, you definitely need to take the B1 English test. This test will be necessary, and it’s not a written test at all.
The B1 exam is actually a conversation test. As you can see, English is the language of the country. So the government can’t really trust anyone who can’t even speak their language well to live in their country. Furthermore, even though if you’ve already had a spouse or partner who lived in England today, passing the test will still be mandatory for you. Make sure you understand that the exam will be a discussion between you and the examiner about a prepared topic. Understand English and the topic well, and you will increase your chance to pass the exam.