Capita and a few other companies have made their business niche going as general contractors for multi-million contracts that are highly toxic.
Must of them have vague specs, are abolutely underfunded for the pie in the sky sold to the MPs. Most of them started as a valid and doable proposal, just to be bloated beyond recognition by various stakeholders.
Capita has a very capable legal/tender department. They sift those impossible tenders and enter a contract that will give them a healthy margin on a incoming train wreck.
They are the ones, where the devil uses a very long spoon.
There a a few more of them around Europe. Some are IT specialists, some construction.
If you get only these carrion eaters in a tender, you should abandon or at least reconsider the scope of the project at once. It is so flawed that it will either never work or need much more money for a minimum viable product.
In our part of the continent, Atos / Worldline is living in the same niche. In Germany there was a proposal and then a law for a special digital lawyer system to send and receive secure (end to end) and binding legal documents. Atos got the bid (only real contender because of the size of that thing).
The original spec were doable and Atos was on the brink of on time and on budget delivery (a money loosing contract till this point).
Then someone realized that the specs did not allow for a attorney suddenly dropping dead / being on vacation. The system was so secure (to spec) that no one, but the original receiver with his smartcard and his passphrase could read the document. No vacation stand in, no secretaries.
After that Atos had to do heavy kludges to get his in. And that was off spec and off the original contract, so they were paid by the hour (ka-ching). After a emergency stop days before deployment there were many further delays. And the system is still not working as envisioned, but working to spec as entered in the contract.
Same in contruction: The new Berlin airport (BER) was designed and the construcion firm gave a bid for about 3.5 billion euro all inclusive to build this airport till 2009.
The states wanted to spent less mony and said, they would plan an build it without a general contractor (they estimated 2 billion).
We are now at 7 billion euro and still have no BER. The companies that were bidding to be general contractors are getting more money now.
This is the reason, no one ever blocklists crapita. They would loose in court, because the original contract was crap, leaky and the project was already sinking before it was signed.