Myself and 2 other guys were playing cards until around 3am on a warm summer night , we were all very heavy [ no not dope ] smokers , i went out onto the balcony [ 3rd floor ] to get some air , i saw across from me [ about 40ft away max ] a black oval shape very very slowly moving from left to right , between me and it was a row of houses , i could not see the bottom of the object [ because of the house blocking half my view ] , only the top which was between 20 =30 ft across ,it moved very deliberately . I called out to my 2 mates , who confirmed i was seeing what i was seeing . To repeat it was soundless , and matt black , it reflected VERY little light from the streetlights , if it was above the horizon it would have been very hard to see . As i said it was only 40ft away max, none of us went down to the street to see it in it's entirety , i convinced my 2 mates that it was a balloon of some kind , why i said that i to this day i don't know why , maybe i was frightened . I know for a fact it was not a balloon , as i was watching it i was seeing a thing that did not waver 1 inch in its course as a large balloon of that size would have had to have some slight up and down movement as it traveled along . This happened in the west kensington a part of london , a very built up area. Over the years i have looked for black balloons without tail fins [ most large ballons i have seen since [ goodyear blimp ect... ] have tail fins larger than the balloons body , still can't find any . The only other explanation i gave to myself was that someone was moving a large balloon at 3am in the middle of london , but that falls flat when i found out that the direction the ''balloon'' was traveling was a cul=de=sac , no motor carrying a large balloon could have gotton to the main road . OF course being human i curse myself for not having the courage to go down and take a closer look at what we saw. Just my luck that phone camaras were not around then. I hope this can help someone . goodluck to all