Actor David Tennant delivered his lines in a low voice while filming scenes for Tv drama Broadchurch on a public beach because he feared passers-by would overhear the top secret plot.

Tennant and co-star Olivia Colman play cops trying to nail a child killer in the hit British show, and many scenes for the second season were shot at a seaside resort in the south of England.

However, the former Doctor Who actor was so concerned that members of the public would hear his dialogue and work out the plot that he deliberately dropped his voice to a near whisper.

Tennant tells U.K. talk show host Graham Norton, "It was tricky because people knew what they were looking for this time and we attract a certain amount of attention. You are very aware when you are out doing a scene on the beach or at the end of the pier that there are people licking ice creams two feet away from you! I think, 'I can't say this loudly or it's all going to be given away'."

The second season of Broadchurch began airing in the U.K. earlier this month (Jan15).