@Colin Barron - What you're referring to is the basic rule of the Single Market: the amount of access you get to the Single Market is proportional to your alignment with the rules that underpin the Single Market. The Johnson Government trying to present the basic principle of the free trade zone (in fact, the basic principle of
any free trade zone) as a point that may be negotiated away is exactly what I'm talking about: they've been drawn to play Real Madrid, but their strategy is basically to insist that the offside rule should be waived for their team only, so that they can walk off without defeat when such an unrealistic demand is not met.
The rules of the Single Market are clear, and were never up for change. It was up to the UK negotiating team to work within that set of rules and concede access in some sectors in exchange for more complete access in others. Negotiations with other nations will follow exactly the same pattern. That's a hard job, and it will produce winners and losers domestically, and that's why the Tories are avoiding it.
It'd be funny seeing the Tories pretending to care about the fishing industry if the consequences weren't so serious. The UK imports two thirds of its domestic fish consumption, and exports 75% of its fishing catch. Current EU membership gives the UK access to 30% of fishing stocks in its waters. (those are UK government figures). So, using facts, let's do some maths. There's plainly a domestic demand for 7.5% of the UK's national fishing stocks (that's the 25% of the available 30% that UK boats catch that doesn't go abroad), so the livelihood of fishermen depends on the ability to sell the much larger portion. Being able to double the amount of fish landed will not increase the domestic demand for that fish because the two-thirds that are imported are species that are not caught in UK waters, so cannot be substituted. So, unless there's easy access to export markets (of which the EU is by far the largest, and the only practical one for fresh or frozen fish), you'll have a glut that will drive down prices and push small fishermen out of business.