The Treaty of Birgham, also referred to as the Treaty of Salisbury, comprised two treaties intended to secure the independence of Scotland after the death of Alexander III and accession of his granddaughter Margaret in 1286.
In reference to the above point that the treaties of Birgham and Salisbury are one and the same. This is not accurate. The treaty of Salisbury was concluded in 1289 and relates to the arrangements by which Edward I would secure the transport of the Maid of Norway from her homeland to Edward's own custody until Scotland was made safe for her to take up her right as queen. The Maid's father, Eric of Norway, while keen for his daughter to take up her right in Scotland had been concerned for her safety given the political instability in Scotland. Edward I was able to broker her transfer from Norway, assuaging Eric's fears with his own personal guarantees for the infant girl's safety and also settling the matter of the outstanding dowry payments which Alexander III still owed to Eric for the marriage of his daughter to the Norwegian king.
Guaranteed by Edward I of England, the purpose of the treaty was to put to rest the competing claims of the House of Balliol and the House of Bruce. The treaties were drawn up in Salisbury in 1289 and Birgham, Berwickshire, in 1290. They were negotiated and signed by the Guardians of Scotland, who were ruling in Margaret's name due to her age. Under the condition that Margaret would marry Edward's son, Scotland was to remain "separate and divided from England according to its rightful boundaries, free in itself and without subjection." The treaty specified that even though a wife's possessions should become her husband's upon marriage, in this case it would not. It stated upon Margaret and Edward's marriage that the churches of Scotland and England were to be made separate, that the owner of lands in Scotland shall not have them disinherited. It made sure that both the parliaments of England and Scotland were to remain separate and not be held outside of their respective country.
The treaty proved ineffectual, both because Margaret died en route to Scotland in 1290, and because English negotiators had included enough reservations to render the independence clauses useless. In 1291 Edward summoned the Scottish nobles to meet him at Norham-on-Tweed and styled himself overlord of Scotland ('Lord Paramount of Scotland') and challenged claimants to the Scottish throne to recognise himself as a feudal superior as a condition of his agreeing to arbitrate the various claims.