Do GM crops cross-fertilise with non-GM plants?

There may be individual cases of cross-fertilisation, but these are the exception.

In Europe, for example, Spanish farmers have grown GM maize next to non-GM maize for over a decade, and there have been no coexistence-related problems through voluntary schemes.

Spanish farmers employ practical measures based on extensive cooperation. These include: isolation distance and rows, planting near other crops, different flowering dates, cleaning of equipment, traceability and labelling, testing, etc.