"lecturer" is a permanent position, more or less equivalent to tunured in US system. It is not wrong to correspond to the associate professor position in US system.

Assistant professor is not a permanent (tunured )position, though it leads to a tunured position.

I asked an american professor educated in England,
who said that there is not exact correspondence. He suggested that

Lecturer, Senior Lecturer <===> Associate professor
Reader <===> professor
Professor <====> University Professor

But he also said that in England different university
has different ranking. And the word 'permanent' is not equivalent to 'tenured'.