I can't imagine London considering getting common hippo. 1.They don't fit with their 'conservation in action' motto. 2. The sealion pool isn't suitable for many reasons and 3. there is no suitable sized house. I can only imagine them having big Hippos again if they had a brand new 'underwater viewing' design, which raises the hippos' display value by about 99%. But I can't see it happening there.