Accepted a long term supply role 2 weeks ago, have handover dates booked for next week, starting with them April but want to cancel it all? Is it very evil to tell agency I do not want to work there?

It doesn't work like that if you have a good working relationship with them.

They want to keep their good supply teachers and will bend of backwards to keep you and give you what you want.

Depends on supply and demand.

Lots of jobs - it's worth them keeping you onside so they can make their commission
Lots of teachers - you have lost them a booking and will go to the back of the queue

Number one rule of subbing- you work where you want to work.
Number two rule- put yourself and your own mental health first. A poor school/ class/ smt can break even the strongest teacher.

Give them your reasons.

I've heard so many stories of supply teachers just not turning up or going out for lunch and not coming back in the afternoon. You telling them you don't want to work there and giving notice of that is small fry!

No TA in year 1? That is not legal. Second red flag for me is any long-term post for the summer term as you will be lumbered with writing reports, when you will have only had them for a couple of months. Moreover, you still might not be paid to scale as this legally can only be enforced after 12 weeks.

As for feeling you are letting them down, do not fret. No school has any qualms about letting a supply teacher go when budgets get tight if they can cover internally.

Can you contact schools you’d like to work in directly? Agencies are a compete financial rip off for the teacher involved.
In NI subs are booked directly by the schools via a website called Nistr. They pay the full daily rate to the teacher cutting out any middle man.

Supply can be brutal. A school can cancel a booking with very little warning and no explanation so I wouldn't worry too much h about whether or not it's evil.

This.

I can guaranteee that, if the school no longer needed you, they'd just cancel the booking without any consideration for you or how it would affect you.

Supply can be brutal. A school can cancel a booking with very little warning and no explanation so I wouldn't worry too much h about whether or not it's evil.

However, you may find that your consultant thinks you're flakey and won't offer you other bookings so quickly.

It's in their interest to have a good relationship with the school so their priority will be to cover the booking rather than find something that you'll like

I wouldn’t take on that level of responsibility if I wasn’t a permanent member of staff. You’re getting all the crap without the financial stability. Turn it down!

No, YANBU

That's the beauty of supply.

You don't have the security, pay or progression of a permanent member of staff. They don't have the reliability and predictability of a permanent ember of staff.

Some will say its unfair on the children but you are important too.

I did supply for a good few years and always did long term roles. I only ever once cancelled a job part way through because it was affecting my health as the school was a really poor fit for me. The agency was fine about it. They had someome else in there the following day. I took the rest of the week off and was back in a new long term role the following Monday in a great school, which I loved.

From what you've described, the new job sounds very normal for a teacher. If that's not for you fair enough, but you'll probably come up against this scenario quite often if you're looking for teaching jobs.