Introduced into the TCPA 1990 by the Localism Act 2011, planning enforcement orders (PEOs) are a powerful tool for local planning authorities (LPAs) seeking to enforce against breaches of planning control. In cases where matters relating to an apparent breach have to any extent been deliberately concealed, a PEO allows the LPA an extension of time – 1 year and 22 days, known as the enforcement year – in which to start enforcement proceedings: see ss 171BC(1) and 171BA(3) TCPA.
LPAs must apply to the Magistrates' Court for a PEO within 6 months "beginning with the date on which evidence of the apparent breach sufficient in the opinion of the [LPA] to justify the application came to the [LPA's] knowledge": s 171BB(1) TCPA.
The LPA is able to self-certify this date under s 171BB(2), a certificate being "conclusive evidence" of the fact of the date. Based on the clear legislative language, Parliament evidently intended to allow LPAs the highest degree of discretion to decide when time began to run for the purpose of the application.
However, the case-law is not so clear. The leading case of Tanna v Richmond LBC  EWHC 1268 (Admin) provides that a s 171BB certificate is normally determinative but may be challenged if (a) there was a fraud or (b) the self-certification decision was clearly or plainly wrong (at paras 33-35). In determining whether a decision is clearly or plainly wrong, Collins J believed that a "clearly material" test is whether the decision "was one which could not meet the test of being a reasonable decision" in judicial review terms (paras 35-36).
If misinterpreted, these remarks can give rise to considerable difficulty in practice. Respondents tend to interpret them as an invitation to challenge the LPA's certificate by showing the Magistrates' Court that the decision was unreasonable in public-law terms, usually by taking the court through a lengthy and detailed analysis of the LPA's investigative history in a bid to prove that the LPA had sufficient evidence of the apparent breach at a materially earlier date than the one certified.
This interpretation of Tanna causes all manner of problems, not least that it generates time-consuming and costly satellite litigation and undermines the clear language ("conclusive evidence") of s 171BB(2). It is also at odds with cases considering identical provisions in other legislation. Most recently, in Chesterfield Poultry v Sheffield Magistrates' Court  EWHC 2953 (Admin), Males LJ and Jefford J interpreted clearly/plainly wrong more strictly, to mean "plainly wrong on its face and patently misleading" without any reference to extraneous evidence (paras 31, 40). On this reading, a forensic dissection of the LPA's investigative history in order to overturn the certificate is out of the question.
This stricter approach is surely correct. Parliament could scarcely have been clearer in its language under the TCPA. It is vital to read Tanna in its proper context.
Dr Alex Williams is a member of the Cornerstone Barristers Planning & Environment team. He has represented LPAs in PEO proceedings. This case update is a summary of arguments that can be read in full in the Journal of Planning & Environment Law, at  JPL 224-230.