Hi Chimevault
B2B: yes UK company can be the importer of record and pay VAT+duty on delivery on orders above and below 135 GBP
B2C:
above 135 GBP private consumer can be the importer of record and pay VAT+ duty on delivery
below 135 GBP No consumer cannot pay upon delivery. You need to charge VAT at checkout and register for VAT # in the UK and report this to the UK tax authorities and pay back the VAT. (However they are working on some new exceptions where in the future mail carriers and/or the shippers might assume VAT responsibilities if they wish to.)
Those are just very general simplified guidelines. If you are a U.S. or Canadian feel free to google Euro VAT Refund and call us in Los Angeles. We are happy to explain more.