There are rules on the content and origin of the goods imported to avoid what you say - that´s international trading 101.
What you say works partially if the UK uses the opportunity to get that said meat cheaper than in the EEU, make it ha processed food in UK and then export it to Europe, as most of the added value would be on the UK processing in that case and would comply with the origin rules - but the margin would be much less.
australia are importing wine in large tankards to the UK. the UK bottle it and promote it as australian wine bottled in the UK.
its then sold in the EU without tarrif. meaning australia save:
20% on tarrifs
save on breakages in shipping because they dont bottle it in australia any more.
america send chicken to the UK. it is then breadcrumbed and sold as southern fried american chicken processed in UK
america saves tarrifs when then selling it to the EU
other examples are electrical components sourced all over the world and then making phones/devices in asia. asia ship it to the UK so they can upload english firmware and package it in shiny boxes. its then deemed british produced and sold to the EU
there are many things that also need just paperwork administration to get a 'change of origin'
normal customs ports(dover) have very strict 'origin' requirement proofs. which is why dovers port is having a headache this month. but freeports are designed to bypass those headaches..
.. hense why they are an actual thing thats suddenly in demand again
remember that a freeport is not the same customers port as dover. as thats the point