Another 'what flew over' question.

[Deptford Draylons]

Anyone know what flew over High Halden in Kent around 1015am today ? I was in my parents garden and a fast jet went over fast and I presume very low, so much so I didnt even see it. I was guessing 500 -1000ft , the elderly chap next door said it was so low he thought it was more like 100 ft.
Anyone ?
Thanks