Was it a 'big cat' in London?

Every now and then we receive a handful of 'big cat' reports that seem just a little strange - mainly due to the fact that they are said to have taken place in an extremely built up area. London is, of course, an incredibly crowded city, but there are a few large green spaces dotted about the place, even so, how can we explain the following possible sighting of a 'black leopard',

"I was walking to work in New Cross South London and looked to my left and saw a long black tail hanging down from the roof that covers the bins outside our block of flats. I then looked up and saw the biggest black cat i have ever seen - this was no domestic cat. It was very built with strong large leg muscles/joints that you could see very clearly from the rear view. It was just perched with its tail dangling down.
I completely freaked out and ran so fast as i was the only one in the area at the time and terrified of being spotted by this animal.
I have reported it to the police, who checked the area and can no longer find it. (They had suggested it was a large stuffed animal) - i guess we can now definitely rule that out.
I am disappointed that I wasn't taken more seriously by the local police who asked me almost straight away if I had been drinking when I first reported it.
The point is I was a meter away it was perched just above me and it was morning so I did not see this in the dark or at some distance and it was intimidatingly big.
The thought that it is now roaming around somewhere in the area is very scary and I am very nervous to walk home. "

One only has to look at a map of New Cross to realise how built up this area is, most London-related sightings tend to come from towns such as Bromley, but when one considers that in the past there has been sporadic reports at Nunhead, Dulwish, Sydenham, it is clear that these areas are part of one particular animals territory. Little else is know from the sighting, maybe the witness got it wrong, as so many seem to do, but a large, predatory and very elusive cat moving at night could simply end of anywhere when one considers the network of tunnels, alleyways, back streets and green areas that run through London's outskirts. However, due to such sightings being so sporadic it is difficult to pin-point any route this animal would take and due to a lack of consistency we have to wonder just what people are seeing.

Some witnesses are adamant that they are seeing large exotic animals, in this instance we can only file the report, look around the area, and hope that more sightings occur.