What were those multiple flights leaving London night of 29th Aug 2019? First time post here, please let me know if more detail needed (and which tag would suit it best).

I live in Essex UK, in the evening normally see lights of planes on approach to the London airports.

This evening (29 August 2019) from 21:00 BST / 20:00 UTC I have seen lights of planes flying away from London in large numbers (at least 30 when I started paying attention).

They were in groups of about 5, then another group following not far behind. They appeared to be heading in an easterly direction away from London.

Could someone help to shed some light on this? Have lived in this area for 15 years and never seen anything like this.
Nothing stands out on Flightradar24 for that time period by using the playback function. So most likely they're not civilian.

What I found was a military-related NOTAM via notaminfo.com/ukmap:


  MIL EXER. MIL PARACHUTING AND HELICOPTER HOIST OPERATIONS WI 5NM
  RADIUS 515900N 0012500E (BAWDSEY, SUFFOLK). FOR INFO 01638 545012.
  2019-08-0649/AS3
  
  FROM: 29 Aug 2019 18:30 GMT (19:30 BST) TO: 30 Aug 2019 00:30 GMT (01:30 BST)


The time matches if we account for padding, and the drop area would make them fly west to east to arrive at Bawdsey, depending on their base and your location.

If too concerned, you can trying calling the number quoted above.