Complex sentence: The "Daily Mirror" reported that Tennant was forbidden from attending "Doctor Who" fan conventions while playing the role, to avoid the chance that Tennant could accidentally let slip any plot points during filming of the series.
Split into simpler sentences: The "Daily Mirror" reported that Tennant was forbidden from attending "Doctor Who" fan conventions while playing the role. This was done to avoid the chance that Tennant could accidentally let slip any plot points during filming of the series.