[Wales] Landlord refusing pet scorpion

Per the part of my contract stating:

"You must obtain permission from the landlord to keep a pet at the property. Please contact [company] for consent. Please note that if a pet is agreed at the property, you will be asked to sign a pet policy and a higher deposit for any damage caused"

I recently contacted my landlord regarding a potential pet scorpion, detailing how it is a completely harmless and non destructive species (genuinely incapable of causing more damage to the property than a pot plant - or more discomfort than a bee sting, if someone decided to stick their hand in there and try to hurt it) and how it would be safely confined. I was responded to with a flat refusal, that they were "unable to authorise" pets at the property. The scorpion in question is about 3cm long and captive bred (thereby does not carry the risk of parasites that wild caught specimens do); I'm wondering whether I should contact the landlord again stressing this, and offer to pay for any damages it somehow causes, or whether the landlord should be providing solid justification for refusal? Could it also be difficult to evict me based on a 3cm long creature that exists in a sealed plastic box of plants? I'm weighing up the option of keeping it a secret, but I genuinely do want to be completely above board with everything. I already was in possession of the enclosure, and the species in question is usually difficult to obtain, so this is particularly frustrating. Thank you for your time!