For clarity, my salaried staff are not contractually entitled to overtime, but i am aware that other companies can and do have different arrangements.where do you get the idea that "salaried staff CANNOT receive overtime"
They Can.
However it's not a legal obligation to pay them, but if you make an arrangement, it's fine.
"Salaried employees typically do not receive overtime pay. But a salaried employee can receive overtime pay if an agreement between him and the employer has been established; this rarely occurs. An employer is under no legal obligation to pay overtime to salaried employees."
https://www.pocketpence.co.uk/rules-paying-salary-5367027.html
However, in my company's case, salaried staff didn't get overtime so weren't entitled to make a retrospective holiday pay claim.