Looks a bit steep.

I think it should be 20% VAT on the poster plus 20% VAT on the shipping cost plus the Royal Mail handing fee.

Came via USPS
untied states postal service

I'm in Ireland and recently got stung for around €30 in duty for a Shephard Fairey print from the US. Not the end of the world, but UPS charged me nearly the same amount again for the privilege of them paying it up front on my behalf as a service fee!

I have had the same and sent the following to the company and they have always resubmitted an invoice without their “handling charge”. They will try to recover their costs but they have no authority to have charged you. However you are obliged to pay the duty. Maybe they prefer to settle on their likelihood of receiving the larger sum, being the duty and in your case maybe this might save you the a significant portion of the £25? As I say this has worked for me and is UK specific so offer this wording without prejudice. I would credit whomever but cannot recall where I came across similar and hope it helps you. “Dear xxxx,
This is in reference to invoice #(enter no here)
After having bought the posters from (enter country of origin) , I understood there would be the possibility of VAT due on receiving them.
I was however surprised to see an additional section for a clearance administration charge of £12.
Since (enter country of origin) is outside of the EU, I of course will pay the VAT due.
However, I refuse to pay the clearance admin charge of £12, since at no point was I made aware of, nor did I agree to, any terms and conditions which clearly stated that I would be liable for any such charges.
At no point in the transaction and subsequent delivery was any contract for a clearance administration charge made between (enter delivery co) and myself. My understanding is that it is not permissible under UK contract law to levy charges without prior agreement or a contract. I paid the supplier for delivery, and would expect that any international clearance fees be factored into the initial cost of such a shipment.
If you want to pursue further charges for delivery or administration or the terms upon which goods are shipped, I suggest that you take it up with the company who shipped the goods initially.
Therefore, I request that you update this invoice to reflect no admin fee, and once that has been done I’ll make immediate payment.
Please let me know when this has been done.
Kind Regards,”

With the original post I made the assumption the courier had already delivered as had been the case with my experience. More specifically this is where Fedex had delivered and then they subsequently invoiced my home address- I have not had experience with Parcelforce and guess if they still have your goods then they may well have you by the short and curlies. What a pain!