Restrictive covenants

[JC70]

My house had a restiction when it was built 40 years ago that the front garden be kept as grass with no fencing or hedging. I believe the developer had gone bankrupt several years ago, does this mean the restriction is now null and void? How would I found out if there was a successor? The rest of my estate built at the same time has many fences and hedges now, so I would like to know where I stand for erecting a fence.