By convention, Members of Parliament cannot directly resign from their seats. To bypass this rule, MPs apply for one of two historic, unpaid positions with no actual duties: the Steward and Bailiff of the Chiltern Hundreds, and the Steward and Bailiff of the Manor of Northstead. Accepting either title automatically disqualifies an MP from Parliament, allowing them to step down.
This legal workaround originated from the 1701 Act of Settlement and the 1707 Act of Union, which banned individuals who held ‘an Office or Place of Profit’ under the Crown from serving as MPs. While the measure was first introduced to limit royal influence over Parliament, MPs soon realised that applying for these effectively defunct offices with little or no pay or responsibilities offered a convenient way to vacate a seat. Today, MPs must request to be appointed to one of these positions, which is by precedent approved by the Chancellor of the Exchequer. The Chiltern Hundreds was first used for this purpose in 1750, followed by the Manor of Northstead in 1844.
To find out more, Dr Martin Spychal has gone into more historical detail of the practice in this article: How does an MP resign? The Chiltern Hundreds & the Manor of NorthsteadHow does an MP resign? The Chiltern Hundreds & the Manor of Northstead