The Highway Code used to mostly say what was considered safe etc on a road and had very few 'MUST' or 'MUST NOT's in it.
This meant that drivers were not immediately breaking the law for doing something which, in their particular circumstances, was sensible even necessary but is illegal.
Almost all dangerous driving can be covered by dangerous driving laws; there is very little need for laws which specifically state what is dangerous or not. There are almost always exceptions.