IR35 tax law came into effect in April 2000 and was introduced to tackle those individuals who were providing their services via a limited company (known as a ‘personal service company’) in circumstances where had the company not existed they would have been taxed as employees.
IR35 is also known as the ‘intermediaries legislation’. 
How to determine if you are among the disguised employee IR35 is talking about? Here is our Check-list.
Introducing the IR35 Forum and BETs
In 2010, the legislation appeared to be over complicated and confused. They decided to introduce the Office of Tax Simplification, a team of tax experts and treasury officials that were set to reviewing the IR35 legislation.
A lot of Improvements were made allowing more guidance and introducing the IR35 Forum and BETs in answer to help contractors to understand this piece of legislation.
Further efforts were made to assist contractors with understanding IR35 and self-assessing their risk of investigation from HMRC, with the introduction of the Business Entity Tests.
The tests work on a point scoring basis, landing a contractor either in low risk of investigation or medium-high risk. If found to be low risk, a contractor could provide the relevant information to HMRC and be guaranteed a three-year investigation-free period, providing circumstances remained unchanged.
These were widely criticised as being wildly unhelpful, as most genuine contractors would naturally land in the medium-high risk category and they could not be used to actually determine employment status.
In the same year, an amendment was made for contractors whose end
clients are in the public sector, such as the BBC and NHS. It was declared that any public sector contractor with a contract lasting six months or more and earning £220 per day or higher is required to provide their client with the assurance that observes the IR35 criteria.
A year later an amendment was made from the Finance Bill saying that officeholders who take on management roles in their client’s business, will have to apply IR35 for tax purposes.
This change was made to stop high-profile senior level management of government bodies operate through service companies.
The off-payroll rules reform
At Summer Budget 2015 the government announced the intention to reform the off-payroll rules in response to widespread non-compliance. This measure moves responsibility for deciding if the off-payroll rules for engagements in the public sector apply, from an individual worker’s PSC to the public sector body, agency or third party paying them.
After considering the issues, the government announced proposals to reform the rules.
From 2017, where a public sector organisation engages an off-payroll worker through their own limited company, that organisation, will become responsible for determining whether the rules should apply, and, if so, for paying the right tax and NICs. 
Draggin-in the private sector
With the beginning of 2018 it was expressed the intent to extend the rules to the private sector, as Philip Hammond announced:
“The off payroll working rules are designed to ensure fairness.
Last year, we changed the way these rules are enforced in the Public Sector but widespread non-compliance also exists in the private sector.
So following our consultation, we will now apply the same changes to private sector organisations as well starting from 2020” 
We can defiantly say that 2020 will be the most important year in the history of IR35, which will shape the future of flexible working in the UK.
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 https://www.thefriendlyaccountants.co.uk/ir35-changes-from-6-april-2017/ https://www.qdoscontractor.com/news/2015/02/19/why-ir35-the-legislation-s-origins-and-developments