...the Michaelmas site (which was hacked just before we signed them up) has 'seemingly' replaced kicked another of our customers ranking for this key phrase and replaced it...
The above is much more specific than your original post, and I'd have to say that it is too precise a match to be coincidental.
Since the Michaelmas placeholder currently has no text content, its rankings must come from inbound links pointing to www.michaelmas.co.uk.
Conceivably, your football site's domain name server got hacked and links that were pointing to your football site have been redirected to michaelmas, but I assume you'd see that redirection in a browser if you entered your football site's domain name. Check the football site's domain on a server header checker, and make sure it's not being redirected to michaelmas.
I should add, with regard to my theory, that if it were some kind of odd co-occurrence effect, that the present setup of no distracting text on the Michaelmas place-holder page might be an ideal "blank canvas" on which to see the effect I'm supposing... ie, with michaelmas being the common word in the phrase posting list that also includes a bunch of football terms.
I'm tending to think now it's more likely a "crossed wire" somewhere in the hosting or dns than in Google's phrase posting list... though conceivably there's a combination of both going on, skewed by the word "michaelmas" that might have effectively become a kind of football "brand". This is very similar to one of the strange results I've seen recently, so similar I was assuming yours was another.
It's late at night here, so I need to leave it at that for now. I'd check into what's going on with your other domain's dns.
Meta tags on a page, incidentally, really don't have any effect on rankings. The page "title element", in the head section but not technically a meta tag, can be very influential in page rankings, particularly in conjunction with inbound linking and onpage text.
Why, btw, have you gone to a place-holder page about your hosting company rather than a temporary page identifying Michaelmas House with some temporary content related to them? WhoIs does show that they'd had a site up before. I'd hold off making any change for now, until you diagnose this problem, as text on the page might mask whatever is going on.