However, if the person is an heir presumptive, or if the peerage has no subsidiary title, then Master/Mistress is a common styling.
However, because the word Mistress is quite archaic, many women choose not to use the style Mistress and instead use the regular styling, e.g. Lady Mary Smith or The Honourable Mary Smith.
As a result, Masters were ineligible for election to the British House of Commons for Scottish constituencies after the Acts of Union 1707.
Members of Parliament would be disqualified upon becoming the eldest (living) son of a Scottish peer, and a by-election would be held for the vacant seat.
This practice was ended by the Scottish Reform Act 1832, and the Masters could be elected MPs like their English counterparts thereafter.