I would suggest that the date of a winter ExiliCon in Manchester should be chosen with some care.
First, it probably should be after the middle of February, to try to avoid problems with the weather (snow, storms, etc.).
Second, if (and it's quite a big if) you want the convention to be a "shop window" for Exilian, I think it needs to be before the end of university term time. Manchester has many thousands of students, which probably translates to at least some hundreds interested in the things Exilian does. There are probably RPG and other games societies that would be willing to advertise a convention to their members.