The Enquirer has been shown emails by angry trade contractors who have been told to sign-up by the end of the week or have their deals ripped-up.

Carillion courted controversy earlier this year when it asked subcontractors to discount 20% from its bills.

One subbie told the Enquirer: “It’s not an option – you either discount or they won’t give you any work.”

A Carillion spokesman said it selected its preferred suppliers on “a myriad of requirements” including health and safety, quality, reliability of delivery, and pricing.

He added: “It is a competitive market and if suppliers offer discounts, and some instances double digit proposals, this sets a benchmark for other suppliers.”

The demand seen by the Enquirer states that all suppliers who have not signed-up with Carillion’s online bidding system by Friday will “no longer be able to work for Carillion”.

The source said: “I’m wondering whether that’s a bad thing at all considering the terms they are implying.”

The Carillion spokesman added: “Supplier terms are ultimately determined by competitive tendering, including e-auctions, not by Carillion.

“The best suppliers set challenging benchmarks for the others.  Suppliers are selected using an extensive ‘score card’ covering everything from quality, reliability of delivery, health and safety, and sustainability, as well as price and value for money.

“For many goods and services, factors other than price are the main determinants in choosing suppliers.”