There is a come-back, you can challenge it in court and would likely win if you could prove the knife was legal under UK law
My opinion & outline experience is that this comeback is nothing more than theory for many folders & even fixed blades. I’ve challenged the UKBA on the restoration side of seizure. The magistrates court challenge is a condemnation proceeding. Failure to establish the knife type as falling within word of law versus interpretation / spirit of law & with virtually no case law or defined legal precedent will leave a magistrate at the mercy of the clerk of court & the weight of HMRC C&E BFDU acting upon open definition of switchblade, Gravity knife & Zombie knife act.
Anyone who challenges the condemnation proceeding & wins in court does not set a precedent either. I am aware of no successful challenge to condemnation proceedings. If you lose, you are liable for your & their costs. I was given advice that I could be lumbered with £15k in costs, further appeals by either party notwithstanding !
I went the restoration route rather than condemnation proceedings challenge. I lost.