Since UK is in EU no visa required.
Your friend has a right to live and work in the UK (let alone Scotland) and so doesn't need a visa
Polish citizens can work in the UK so he certainly wont need a visa, but you might !
In the event you cant be routed in transit, (I am not familiar with Glasgow airport so dont know if this can happen there), then if you have to go landside, your visa will very likely be granted unless there is something highly unusual about your circumstances.
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