The Alien Act was a law passed by the Parliament of England, in 1705, as a response to the Parliament of Scotland's Act of Security of 1704, which in turn was partially a response to the English Act of Settlement 1701.

The Alien Act provided that Scottish nationals in England were to be treated as aliens (foreign nationals), and estates held by Scots would be treated as alien property, making inheritance much less certain. It also included an embargo on the import of Scottish products into England and English colonies - about half of Scotland's trade, covering sectors such as linen, cattle and coal.

The Act contained a provision that it would be suspended if the Scots entered into negotiations regarding a proposed union of the parliaments of Scotland and England. Combined with English financial offers to refund Scottish losses on the Darién scheme, the Act achieved its aim, leading to the Act of Union 1707 uniting the two countries as the Kingdom of Great Britain.

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