I'm a doctor applying to a UK visa for an examination. I am employed by the university hospital in my city but I also work in several private hospitals where I earn several times the salary I receive from the university. How can I explain that in my visa application? There's only one "employer" slot and I think it should be for the university job. How then, can I explain my other earnings? Should I state that I am also "Self-employed" or should this go under the "other incomes" sections? Also, Do you think there'd be problems with my application since I receive my private practice income in cash directly from the hospitals and deposit it in the bank myself every month? specially, since that it's about 6 times the official university salary. Also, I may not be able to provide evidence of payments from some of these hospitals!
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But in short, include information for all income you have. Copies of contacts, signed letters that this person employed you and paid you X money.
See this comment by @traveller
Start getting evidence for all income and put off your visa application until you have several months’ worth. There are many examples on TSE of refusals due to unexplained/undocumented deposits, 20% is a significant proportion.
Write a cover letter to include this information if there is not enough space on the form, but if at all possible make a note on the form where the information about that money is.
A tax form on which you declare that cash in hand money will help as well, if you do not yet pay tax over it, consider doing so, to avoid problems in the future.