@cindarellasbelly
It sold for 550 in 2011, was the 460 price full market value? Is there any way they actually did something more substantial? I've seen a house flipped in less than six months near me: increase in price of over a 100 grand but they did actually rewire, instal underfloor heating and insulation, and generally do a speedy upgrade so it was turnkey, though if you just looked at the pictures it looked like a paint job.
It was sold at auction after being on the market a while. Certainly they don't appear to have done anything substantial and there was no mention in the previous details of restrictive covenants or any of the other things that can really downvalue a property that could have been resolved quite quickly.
Grade 1 listed so they wouldn't likely have had time to get permissions and undertake anything substantial