Wait, is there a story behind—oh, here it is:

https://www.headingtonshark.com/Home/About ("Hello. I'm Magnus Hanson-Heine, the home-owner of the Headington Shark House. The Shark House, formally titled Untitled 1986, consists of a 25ft-long fibreglass and steel shark crashing through the roof of an otherwise ordinary house on a quiet residential street in suburban Oxford...")

There are noise conditions and a few scenarios that will need planning permission (facing a public highway is one) but generally pretty liberal.

The shark scenario is more interesting, and was I'd say was largely allowed to stay because it was an art installation. They couldn't have built an extension of the same proportions without planning permission.