Sorry to hear about your Dad. I hope he is recovering well.
How much financial support do you think is needed for the event? When you say it would be hosted by your department, does that mean the department needs to be paid for that? Wiki Wednesday's in London are having a difficult time finding sponsors or venues, so it might not be easy, though there are at least a couple of Wikimania sponsors with people in the UK, so they might be companies to consider asking for support. The Foundation, Wikimedia UK, or possibly even another chapter in Europe, might also be able to provide some support.
If by big names, they mean speakers, then you should contact Jimmy and see when he is free and in Europe and set the date for when he can attend. Perhaps they'd count people like Alison Wheeler (chair of Wikimedia UK) as a big name as well?
I also suggest you get Cormac Lawler involved. I think he's based in Ireland. He's a researcher and has been involved with Wikimania and would be a good fit for this, both as a speaker and organizer.
Angela