Then they're not contractors, they're full time employees that you refuse to pay the benefits for. Given this level of cutting corners, I'm not surprised your counterparts are pulling one over on you as well.
Not sure if you are in the UK but there must be hundreds of thousands of people working in this way and being paid significantly more than FTEs even when benefits are taken into account.
The overwhelming number of contracts signed with them are time and materials rather than fixed scope, and usually with some expectation around working hours.
It is a perfectly fair and reasonable way to contract with someone, for instance if they are operating as part of a team for a fixed project period.
No I get what you're talking about, I have worked in the UK job market for many years. You are under this illusion that those people work exactly every day of the year, in which case they might earn more than an employee who gets benefits. Which they don't. Even during good years being able to put more than half a year on the bill is rare. And now look at the last two years and tell me about job security for "full time contractors", go on. Especially when faced with medical issues.
None of that is relevant. My point is that if you accept a time and materials contract with an expected working day clause then it’s unethical to double book time and in no way a reflection on the employer or hirer.
Oh but on the contrary, it's extremely relevant. The fact that it's uncomfortable to your agenda that the basis of your "time and materials contract" is immoral and unethical doesn't make it less relevant - in fact, it makes it exactly the most relevant thing to say about this.
You have an unethical contract meant to remove people's safety and wealth and based off of that piece of paper you expect people to be ethical about it. Come on dude, you can't be this self-contradictory.