Dual-flush toilets 'wasting more water than they save'

Thames Water says design is more likely to leak as Waterwise warns 400m litres are being lost from UK toilets a day

Toilets specially designed to save water are wasting more than they conserve, the UK's largest water firm has warned.

Campaigners have warned for years that dual-flush toilets, introduced as more efficient alternatives that were expected to use less than half the amount of water per flush, are more prone to leaks.