This has never been the case.
To enjoy full rights, you have to have a local office. Tax forms e.g. Hungarian employment tax forms doesn't even accept the UK postcodes as administrative address, let alone grant application forms.
The second also isn’t true - no recertification appears to be required but could be required in the future should legislation diverge.
As well as the actions all travellers need to take, there are extra actions if you’re travelling to the EU for business.
Business travel includes activities such as travelling for meetings and conferences, providing services (even with a charity), and touring art or music.
Entry requirements The country you’re travelling to might have its own entry requirements, or ask you to have certain documents.
Check the entry requirements for the country you’re visiting.
https://www.bloomberg.com/news/articles/2020-12-24/johnson-i...
The deal doesn’t include any mutual recognition of conformity assessment [...] meaning firms will have to pay the regulatory cost of certification twice if they wish to sell their products in both the U.K. and the bloc
People heading to conferences in the UK have occasionally been caught by aggressive immigration officers and deported.
If you're from Western or Northern Europe, or North America, you will often be exempt for tourism, conferences and meetings for similar countries.
But I, and probably you, need a business visa for a simple meeting in Moscow.
It's up to each EU country what requirements they put on British visitors, but it looks like at least some will require visas for at least some types of business.
Some limitations which I do know of:
* British nationals can’t live and work freely on Europe, so an architect based in London can’t jump on a Eurostar and take a business meeting in Paris by default, they would have to get a visa specific to the country and activity. And their professional qualifications may not be recognised, so would have to operate through local professionals (not sure how that would work in practice).
* Products sold into the EU will have to be recertified for that market, no assumption of regulatory compliance or compatibility. So a lot more red tape and checks in moving products across borders, in particular that will impact food and products built as part of just in time supply chains.
* No ability for British firms to operate in other European countries with equivalent rights as a local company, will have to form subsidiaries instead in many cases.
Would be interested what else people can add.