Sole trader tax problem

I work as a sole trader for a number of firms , I supply and erect access scaffold .I invoice with my unique tax reference number on my invoice and split the invoice 60/40 labour hire . One of my customers has told me this is wrong and stops 20% of the whole amount. I have explained that the 40% is tax free as its on the hire but was told that I own it so it's not hired. There is a tax issue and I think I am owed by hmrc £8 in every £100 that I have invoiced this customer .
Any help please as I do not want to loose customer or get into tax problems.

all companies charge hire on the scaffold and its in every quote i have ever done. Does the company think you give him a scaffold for said amount and if he is not finished in the time scale you just leave it up for him ???????

Guymac, get your accountant to write a letter to your client explaining the error of his ways, this way you should resolve all your problems and still keep working for your client

I would agree with that GM as I think Guymac is quite correct. We had a similar thing but it was with the VAT for new builds and I wrote to the VAT man for clarification which he duly did and I brought it to the customer who sheepishly agreed to pay it. We have since tried to get clarification on another matter and the only answer we received was check your hand book so I think it just depends on who picks up the question as to how helpful they will be but an accountant should be able to explain the regulations no problem.