I think I know the reason, we call it destination port cost here in China, usually they are port cost, handling fee, reloading fee, etc.
This is because you use a China local forwarder to ship the goods to you, I am sure the forwarder is arranged by your supplier, if by CIF terms, it is just costing them 1-10$ per cbm, some even give free freight to the supplier, and forwarder just put those fee into the debit of buyers(destination port).
The best solution is you search a forwarder locally in UK, in this way the local charge will be much cheaper, certainly, before you working with them, ask them to send you a quote for LCL and FCL, then you just need to give contact to supplier for booking shipping space for shipment, or ask forwarder to contact supplier, you can even ask the forwarder to pick up goods from the supplier and ship to you.
For me, sometime my clients do not have a forwarder for shipping, I will use my cooperated forwarder, but besides asking price of freight, I also ask them to quote the destination port cost, this will avoid them charge too much to my clients. and make happy business.
Regret that it is too late to let you learn about this skills, just bear it this time, and improve it next time when you ordered.
As you are deal with chairs, I would suggest you to buy in container, at least like a 20ft container for FCL shipment, this would avoid damage of the goods, try to negotiate with supplier to load more models, that would be easier for you to sell, as we know that supplier want you to pick up less models and bigger quantity for their easier production.
I've deal with office chairs, not sure what chairs you are dealing with, if you need my help, you can contact me.
