If it was the Police Helicopter it must have gone undetected, as there was no report!
or just surveillance, or insignificant!
............... OR, could be the Council, trying to work out a new traffic system for the Town. 
Only if Wiltshire Police
volunteered the use of the helicopter.

Seriously though, the helicopter has been seen about on numerous occasions, but according to the Wiltshire Police website the last incident was mid-July, whilst the Air Ambulance website refers to the last incident as being in mid-June!!
If they need continued public support, they really should ensure that the public knows the services are required, being used
and any incidents are publicised! How long does it take to put a paragraph on a website??
If
any service was not being used for almost 2 months, people would ask why it is still being paid for!