starting salary is £20kish

I'm looking at £20-35k depending on position and company as a graduate, up to £45k after a few years as a senior with experience

But fin, pay is irrelevant in terms of whether a job is "dead-end" or not.

I would prefer a lower paid job with great opportunity for progression than a higher paid job with not great prospects.

My perception of teaching is the same as most of those they asked in the poll - teaching is a bit of a dead-end job.

Hmm.
I have a lot of thoughts about teaching, but my basic observations are this:
You can work your way up the greasy pole to becoming a Head.
On the way, you'll spend less and less time actually teaching, and more and more time doing paper work about teaching.
As a rule of thumb, every lesson you'll prepare is like an iceberg - for one hours teaching time, there's 9 hours prep.
You'll be expected to take on roles that you never studied for, let alone show any aptitude for.
Parents will treat you like a glorified creche owner.
You'll also take on any teaching job you can, as at the moment there's about 40,000 qualified teachers without work, so those jobs you do get aren't going to be the nice ones in small classes with well behaved children.
And between all of this, you'll be expected to act as a counsellor for colleagues and pupils.

Teaching is what it is. If you're the sort of person who wants to be a CEO of a multinational, it's the wrong job.
Teaching doesn't need two-thirds of graduates to want to teach, it needs the one third who are going to do the job with their eyes open to the pile of dung it's become, and love it anyway.
There are any number of jobs you could substitute 'teaching' for in this headline, which doesn't mean anything.

All of this is true. I speak from decades of observation. Both my parents were teachers, and my other half is too. It’s a job for which there seems to be very little adequate preparation, but shed loads of people who think they know the job better, but who are unwilling to take on the job itself.

That's true of a lot of jobs though if you think about it. In most organisations the career progression goes from 'unskilled' to 'skilled labour' to 'management'. The result of that is you gain the skills to be able to do a particular job (build walls, program web sites, whatever) over time but, eventually, the only way to get more status or to earn more money is to abandon those skills and move into management and administration, which is an entirely separate job for which you could have little experience nor the correct skill set.

I've always said a smart business hires managers who can manage and technical staff who can do the technical job, then pays them roughly the same, so a junior manager would have the same pay as a junior skilled worker but they would both have a career progression that would be satisfying in their own fields. One of the problems we have, which has led to jobs like teaching and nursing becoming perceived as undervalued is that we now vastly overvalue the simple act of making a decision while under valuing technical skill. The top end of which is the director of a widget company getting an enormous paycheck for one days work a week 'because he is making important strategic decisions' while the most technically skilled bloke on the shop floor who keeps the machines running that make the widgets gets a fraction of that. On an objective view, which is actually a more valuable asset to the company?