CUOSC, meanwhile, said their representatives were "fully involved in the discussions and decisions leading to this arrangement with EWM".
Neither Day - said last year to be worth £1.05bn - nor his business have so far commented.
It covers Brunton Park, and land to the west and north of the ground, adding that the arrangement contains fixed and floating charges and negative pledge.
That covers both specific and changing assets of the ground, while a negative pledge means United are unlikely to be able to secure any loans against the ground from other parties, or take other actions that might jeopardise the security of the EWM loan.
The Companies House information was not initially accompanied by any announcement from either the club or the EWM.
Day, a former Blues director, was last April ranked 110th in the Sunday Times rich list of the UK’s wealthiest people.
The national newspaper also claimed he was the seventh wealthiest man in the north west, after his assets increased by some £300m.
The timing of Day’s apparent involvement is intriguing, coming less than a month after the Blues ended 650-day talks with a mystery overseas “billionaire”, who has yet to be named.
The latest development also comes as the current United owners face renewed criticism from a section of the Carlisle fanbase, some of who have protested against the regime at the last two games.
The EWM arrangement has also been struck before the Blues’ accounts for the 2015/16 season are filed, with the figures due before the end of this month.
They are still expected to show considerable debts to co-owner Andrew Jenkins and his firm Pioneer, while there has been recent speculation that the Blues have been in need of a significant short-term cash injection.
Day, who has a home at Edmond Castle near Brampton, has previously spoken of his affection for United.
But speaking to our sister paper The Cumberland News in 2010 the businessman, who grew up in Greater Manchester, played down the suggestion he would ever like to own the Blues.
He said: “It’s not my intention in any way, shape or form to get involved in owning a club.
“But I’ll continue to help in any way I can.”
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