In my opinion, the EU's biggest fear is for the integrity of the single market to be breached. That means the UK being able to have unrestricted access in the single market without any level playing field whatsoever. If you ask me, I can see the EU going for a very conservative deal, which allows tight control over what goes out of the UK and in the EU. In time that tight control might be released with bilateral agreements as seen fit. The EU can afford that, considering that its a huge market with trade deals all across the world. Unfortunately I can see the UK being happy with that.
I think the EU’s biggest fear is that the UK will use state aid and subsidies to peal off high-value, high-skill industries.
For example, the UK Film Tax Relief scheme has been hugely successful in incentivising more and more TV and film productions to shoot in the UK. From the FT:
“An estimated £632m in UK tax relief for the creative industries in 2016 led to £3.16bn in production spending on films, TV programmes, animation and video games — a 17 per cent increase on 2015. The industries’ “overall economic contribution” to Britain came to £7.9bn in 2016, which included £2bn in tax revenues.”
The industry has grown by a further 43% since 2016. It is a huge success.
This tax relief was only approved by the European Commission through the loophole of the ‘Cultural Test’ (even though in reality, producers are not only getting tax relief on cuturally British projects, but things such as Star Wars and Indiana Jones). To some extent, the video games industry in the UK has benefited from a similar form of state aid.
I think the EU fears Britain will look at how successful it has been in using state aid and subsidies to boost its creative sector, and may look to try something similar with other industries, once they are no longer constrained by EU state aid rules. This is particular concerning for the EU where the finished product is not a physical good and therefore cannot be punished/protected via tariffs. If the UK sets itself up as the R&D hub of Europe through tax relief for all sorts of scientific, technical and creative projects, it can then sell and license the technology across borders without having to ever manufacture the goods here. Peel off the top of the value chain and leave the EU as the manufacturing and distribution hub...
After all, it doesn’t matter that Apple doesn’t manufacture its products in the US, it matters that it’s research, design and corporate teams are based there.