Never realised that the small chrome dust caps you buy off the bay actualy oxidise with the sensor valves on the Insignia, only found this out at the cost of the young apprentice tyre fitter snapping one whilst replacing the front tyres, to there cost though.
Has this happened to others on here, if you have these type of dust caps on your car check to see if the come off, if not heat up with boiling hot water and gently undo with a small spanner.