What could this be ?

[Astroscot2]

My Brother In Law sent me these pics yesterday which he took on the night of the 14th.   The images show what looks like a slow moving fuzzy object.  To me it does not look like an aircraft, If you look at its motion it does not seem to be following the direction of the trail on the widefield images,  could it be a rocket venting ? Ive attached the full size images and a crop of the object.  would be interested in hearing your thoughts . 

Location Erskine, Scotland - Looking North - North East

Date 14th April

Time 21:40 - 21:41

Lens 35mm   Exposures 5 seconds each

[VigdisVZ]

I'm going to go with lensflares/reflections. The bubble-like effect on the lower part of the brighter image seems to be related to that aswell. Also because it seems to be aligned along a  line from top corner and opposite lower corner.

[Astroscot2]

Hello, hmm not so sure,  Ive seen plenty of lens flares but this looks quite defined ?

[Carina Lass]

I'm tempted to say Katniss Everdine shooting an arrow through the life dome.

But I'll go with venting -