if a council ranger, police car or CASA vehicle drive past,
Council or CASA - unlikely.
Police, possibly, the location being so close to the airport and particularly if a near neighbour is annoyed/busybody enough and/or aware of the Gatwick business decides to dob you in.
As the link provided above says, quoted again:
If your drone weighs more than 100g, you must keep at least 5.5km away from controlled aerodromes.