Thank you for contacting me about chemtrails, defined as aerial spraying from aircraft.

I can reassure you that the Department for Transport is not aware of any other matter or aerosol being ejected from aircraft, other than normal exhaust products. Aircraft can be observed sometimes leaving trails in the air known as contrails.  However, these are simply the warm moist exhaust from the aircraft mixing with the cold drier ambient air thus producing ice crystal clouds. 

I understand that some other countries have on occasions used weather modification techniques, such as cloud seeding, which causes precipitation by introducing substances into cumulus clouds that cause condensation. However, these techniques are generally aimed at promoting rainfall, and should not be considered geo-engineering – projects used for the purpose of trying to minimise the human impacts of climate change. The UK does not use cloud seeding or deploy geo-engineering within the aerospace sector.

Thank you again for contacting me about this important issue.