The book, which is serialised in The Times today, claims that a sound engineer who tested the cellar’s acoustics found that any noises from the rooms would have been heard by tenants living in the above flats, which were rented out by Fritzl.

The book states: ‘The noises that the tenants thought they had heard coming from the cellar beneath them had been real: the thumping, the moaning, the strange clanking noises emanating from deep underground.

‘But nobody thought to investigate.’