This one is actually true, and the sentence is better than the myth.
What the statute says
The Metropolitan Police Act 1839, section 54, makes it an offence to carry a plank (or ladder, or pole, or other bulky article) along a pavement "in such manner as to inconvenience or obstruct the passengers."
The UK Law Commission confirmed this in Legal Curiosities: Fact or Fable? (2013). It is one of the rare weird laws that is both real and still technically in force, though enforced about as often as you would expect.
Source: Metropolitan Police Act 1839, s. 54 (available on legislation.gov.uk, Open Government Licence v3.0). Checked 25 Aug 2026.