He said although the barrier had proved an effective defence, a tidal barrier was needed further downstream.

BBC: Thames Barrier engineer says second defence needed

Representatives from Caerphilly County Council told the committee that the lack of secure funding year on year is the main barrier to effective delivery of biodiversity action.

BBC: Sustainability committee

But so many strategies are cost-effective today, and they require barrier-busting at every level.

FORBES: Richard Branson's Carbon War Room

Substances that cannot cross this barrier are unlikely to make effective treatments for a brain disease.

ECONOMIST: Creutzfeldt-Jakob disease