AIBU to want payment for fitted items left in my rental?

When I moved into my first private rental there was a nice big mirrored bathroom cabinet which I assumed to be part of the "fixtures and fittings" when I moved in. The LL's agent subsequently contacted me to ask if they could come and collect it as it was left by the previous tenant. I refused as it was attached to the wall and would cause me inconvenience if it was removed. The agent then said well we will send the handyman to collect it and replace it with another. She sent me a picture of one they intended to put in its place but it was smaller and cheap looking. She tried saying that in my lease it stated I must allow access to the agent and their workpeople for inspections and essential repairs. I said I am not taking time off work as this is not an essential repair or an inspection. There is also nothing mentioned in the lease about my having to provide these services for free. This is an extra service and you will need to pay me an admin charge of ££ to cover my time and trouble. I never did hear anything back.

Of course you are not being unreasonable. I am sure most tenants fit additional toilets and then take them with them once they move.

Just standard stuff🙄

This is essentially how it all happened

You don’t have a lot of options. If you take the toilet you will need to replace it as presumably there was one there prior to the one you put in? You would also need to replace ant poles or storage you removed to make way for the new. The lesson is don’t spend on somewhere that’s not yours. You can’t force the new tenants to pay.

There was a thread recently about a LL who found that his tenants had replaced the gas boiler with a heat pump. I don't know how the thread ended but the tenants could hardly take it with them when they moved. If you attach or fit something and then move away it becomes part of the fittings. Its up to you to plan for its removal or replacement before you move out and to make good any repairs. I once left a HA flat fully carpeted because I had no option. I could hardly expect the new tenant to pay so they got a great freebee.

You have no relationship at all with the new tenants; your only agreement is with the landlord who expects you to leave the place as you found it (unless you made other arrangements with the landlord).
I think you’re wasting your time trying to get any payment from The Landlord and you’re definitely not going to get anything from the new tenant.