It’s sharp practice but it’s legal. Ask any self employed people what it’s like getting paid by big businesses.
To do MoD work we have to go through a third party who quite openly hold up our payments for over 2 months. The MoJ can be a nightmare too. At one time it looked like we’d have to go through Carillion who would pay you in 30 days if you gave up 10%, otherwise it was 3 months. Now we all know it was a glorified Ponzi scheme.
If only we could pay our suppliers like that! My cash flow is always the biggest headache.