I was in my garden (SW facing) smoking a cigarette looking at the stars. It was a crystal clear sky with a fullish moon low in the sky behind my house (W/NW) and shielded by high trees, excellent for observing stars. There was small amount of low & very thin cloud to the S & SW. I became aware of a very bright red light low (30 deg) in the sky (NE) that flashed on/off approx every second & was travelling in a straight line (SW to NE). At first I thought nothing of it as it's not uncommon to see Police helicopters hovering over the city and there is often airplane traffic in the sky (until recently I lived in West London under Heathrow flightpaths and I'm well used to seing lights from airplane traffic & Police helicopters at a variety of angles & perspectives). However there were no other lights visible apart from the flashing bright red light - normally aircraft have a green light & a white light in addition to a red light. The flashing red light was way brighter than I would expect on usual air traffic. I would estimate the light to be a mile away and right above Oxford city centre & was silent. I watched the light intently and whilst it flashed off there was no discernible object or outline visible despite the excellent viewing conditions. The light then went behind a clump of trees but did not re-appear - I assume it disappeared or changed course. I had observed this light for about 1min in total. After 5 mins of looking at the clump of trees (the light did not re-appear) I turned my attention back to looking at the stars. I then became aware of another bright red light (exactly the same as the first) that had suddenly appeared low in the sky to the SW in some very thin wispy low cloud. This red light flashed as before & appeared to move NW to SE in a straight line, again about 30 degrees from the horizon and again there was no shape or outline seen during the off phases of the flashing. After 20secs or so this light abruptly disappeared before my eyes and a series of much smaller & dimmer red lights (5-6 lights) began to flash randomly for about 10secs where I had first spotted the flashing red light for the second time. Again no outline or shape was detectable. I waited for some more action for another 10mins but nothing happened so I went inside.I observed these events very matter-of-factly & calmly as I've had a previous 'ufo' sighting 4 years ago that served to get the emotion & excitement out of my system. I'm only reporting it as there are likely to have been many others that saw what I saw - it was so low in the sky & directly above Oxford city centre. I had an iphone on me but I didn't film anything as it was short duration and lights only - I know from experience that camera phones don't process night-time lights too well. Also it was freezing cold and my non-smoking hand wasn't going to leave my pocket!I hope this is of some interest/help