As it had already been determined by earlier rulings that escaped sewage amounted to "controlled waste" within the meaning of the Act and Community legislation, the issue that remained was whether, on the true interpretation of s.33(1)(a), the unintended escape of sewage amounted to a "deposit".
Thames Water argued that the wording of the offence of depositing controlled waste required a deliberate act, rather than an unintentional escape of waste within its control. They submitted that such a construction was warranted as s.33(1)(a) imposed criminal liability on those found in breach. Starting with the word "deposit" itself, it was submitted that a "state of mind was inherent" within its meaning.
The High Court determined that whilst the dictionary definition of "deposit - to "put, place(d) or set down" - offered assistance, its meaning was to found within the context of the offence. Significantly, the offence in question was not qualified by the word "knowingly", by contrast to other offences under the same section. As such, intention was not required.
The court justified this interpretation, noting that the due diligence defence afforded by s.33(7)(a) mitigated the strictness of the offence and conferred an acceptable level of deterrence.
The court was not persuaded by Thames Water’s argument that this interpretation would create an unnecessary overlap with the duty of care to prevent the escape of waste provided by s.34. Thames Water was concerned that the more serious offence under s.33 would be easier for prosecutors to establish.
Accepting the arguments of the Environment Agency (which appeared as an interested party), the court held that s.34 did not apply. This was because Thames Water was not in possession of controlled waste whilst it was in its sewage system; it became controlled waste only when (and because) it had escaped, by which time the duty to take measures to prevent the escape could not apply.
Accordingly, having upheld the original decision that "deposit" includes an unintended escape of sewage, the court dismissed the application for judicial review.