If you experience a situation as a pilot that has safety implications then please file a report with the caa. But think of it this way your not complaining about an ats provider but reporting a situation so that lessons can be learned (on both sides). If you get the opportunity then tell other parties involved that you intend to file a report to allow them to fill one also so that the incident can be fully investigated.
As atc, we fill them in whenever we have safety concerns, it's not personal, it's about working together to provide safe ats.
ST