I saw that on Twitter. I was a bit surprised at the assertion that these plates have never been tested; have a look at Tennants' website:
https://www.tennantsuk.com/knowledge-ba ... ate-guide/
https://www.tennantsuk.com/true-3d-compliancy-update/
There's clearly a distinction between 'gel' and Tennants' 3D letters, though I'm not sure what Tennants' are made of and they look pretty similar. I doubt a police constable can easily distinguish between gel and other plastic.