Ban on MPs from employing spouses at next election
Newly elected MPs will no longer be allowed to employ spouses and other relatives using taxpayers' money.
The new rules will come into force at the next election, expected to take place in 2020, although the 151 MPs who currently employ "connected parties" will be able to continue to do so.
The parliamentary watchdog, Ipsa, said employing family members was "out of step" with modern employment practices.
Many MPs argue partners are uniquely placed to do the jobs expected of them.
The Independent Parliamentary Standards Authority, which processes and polices MPs' expenses, announced the ban as it published a revised version of the rulebook for MPs' claims.
'Fair and open'
Its chair Ruth Evans said Ipsa would stop paying for new staff members related to MPs from the time of the next general election, scheduled for 2020.
"We believe that the employment of 'connected parties' is out of step with modern employment practice, which requires fair and open recruitment to encourage diversity in the workplace," she said.
Ipsa said the crackdown was not due to any abuse of the rules or inappropriate claims. The watchdog also acknowledged the need for MPs to employ people they trusted but said they did not consider "that these can only be connected parties".
"On balance, the need for good employment practice which is transparent and encourages diversity outweighs the benefits which some MPs find in being able to employ connected parties," it said in a statement.
Some 151 of the the 650 MPs at Westminster - almost a quarter of the total - employ family members, including 84 Conservatives, 50 Labour and 10 SNP MPs.
The change follows a consultation in which, Ipsa said, a majority of MPs came out against any changes to the rules, with several arguing that spouses provided "good value for money" as they worked overtime and often went beyond the call of duty.
'Value for money'
Under the revised proposals, a member of staff who begins a relationship with an MP while working for him or her after 2020 will have their contract ended after two years as partner or spouse.
There was anger among MPs at the introduction in 2010 of a limit of one family member of staff in the wake of the expenses scandal, with many arguing that spouses were best able to handle the unpredictable work patterns, long hours and need for absolute trust associated with being an MP's secretary or assistant.
The change led to a sharp fall in the numbers of MPs employing family members, from 32.8% of male MPs and 23.1% of women in 2009 to 26.6% of male MPs and 12.9% of women in 2012/13.
The Committee on Standards in Public Life has backed the proposed new changes, arguing current rules were "not appropriate in a modern workforce".
Research has suggested that spouses, relatives and family friends of MPs are paid, on average, £5,000 more than those with no prior connection. However, Ipsa said the sums saved by the changes would be relatively small.