The phrase "unless allowed" is correct and can be used in written English.
It is typically used to express a condition or exception in a sentence. Example: "I cannot enter the building unless allowed by security."
This effectively means that, unless allowed unaccompanied leave, mental health inpatients will be banned from smoking altogether.
Not all the surviving evictees and their descendants could resettle, unless allowed to live and work at the Diego Garcia base.
When Blake asked Plante if he was 'ready to return', Plante refused unless allowed to wear his mask.
When the Earl of Mar returned with James's instructions that Anne join him in the Kingdom of England, she informed James by letter that she refused to do so unless allowed custody of Henry.
Do not start tearing apart packaging unless allowed.
In other words, don't use "I," "we," or "you" unless allowed by your professor.
That means no throwing parties, no forgetting to feed the dog, and no raiding the refrigerator (unless they allow it, of course).
Unless Sánchez allowed Rajoy to return to power, or accepted a new round of elections, El País would launch a vicious campaign against Sánchez.
He told CNN's honchos he wouldn't show up unless they allowed the audience to react as it pleased, but he needn't have worried.
It seized documents, Deloitte wrote, and made "threats to stop our staff leaving the company premises unless they allowed the company to retain our audit files".
Previously, he had said he would not go unless Cuba allowed significant progress on human rights.
