Yes, I had to check as after posting the initial message I remembered seeing a child walking a ferret on a lead in Penryn. I've never seen one wandering the streets of Oxford though...

They don't appear to make it into the top 10 pets of 2014: http://www.pfma.org.uk/pet-population-2014

Perhaps a ferret adoption drive is necessary! http://ferretshelters.org/