The story of a horse.
We all know some dodgy companies, notably a British registered but Irish owned company decided putting equine meat into processed foods was cheaper than beef.

There was no public safety threat, just monetary and regulatory fraud.
That was IN the single market.
It was caught in Ireland doing SPS checks on products from GB. It turned out, Polish, Romanian,German,French companies were all at it.

It was quickly discovered due to the mandatory sharing of data and veterinarian inspections. It was quickly ended due to common jurisdiction of law. Companies were fined, plants closed, licences revoked.

Governments regulate business because , in the real world, "business" can't be trusted.
That is why a common framework in the single market is vital.

GB wants to sell into that market with NO common framework, NO recognition of standards, NO inspection of facilities, NO equal licencing requirements, NO legal oversight, NO ability of sanction.

Nobody is saying that GB (the state) would engage in malpractice (apart from foot and mouth and BSE) but, companies DO for profit.
The 446 million single market needs protection within and without.
End