People should be allowed to travel outside of the UK temporarily while a visa application is being processed. Whether this be to see family, go on holiday, a working trip etc. They should not be held prisoner in the UK.
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Visa applications can take years. To deny travel for this long while an application is processed is wrong. There have been so many cases where people have not even been allowed to leave to visit a dying family member, go to funerals, weddings, visit their children, etc without risk of their application being withdrawn and having to start the process all over again or be deported. I cannot see any logical reasons for denying travel for valid reasons. It needs to change.