Make purchased domain active

Hi, I purchased a domain which seems to be associated with my site (it appears under 'domains' in site settings), but I can't see how to make it the active domain name. Don't know if it's relevant that it's a .co.uk. While registering there was a note saying it may need to be checked that my organisation (a UK charity) was valid, but that would be 24 hours and it's now been two days.

Is there something obvious I'm missing?

Many thanks.