If you are staying in the same company is it ever a good idea to say the truth as to why you are leaving a dept?

[Islaseat]

I’m in the process of applying for a new job in the same organisation.
My current job is getting me down due to poor management, over work and no support from above. Our team is half hard workers and half lazy bastards who will happily leave the hard workers pick up the slack.
The team leader is also a lazy git who is meant to still pick up emails and be available to take phone calls but since WFH has his phone off, manipulates the email system to take all the easy stuff and delegates the shitty stuff out to the hard workers. The other lazy team members cite issues with the VPN, signal, home WiFi etc to cover the fact they’re having an easy time of it.
The harder workers, due to their personalities are actually working even harder since WFH.
I’ve come to the end of my tether and applied for a different role.
I know the manager (who is big butties with the team leader) will want to know why I’m looking to leave.
I’m so tempted to completely tell all, lay it all out on the table, the laziness, skiving, leaving stuff for others to pick up etc.
Or is it best to just say that it’s time to move on and the new role is simply more appealing for my development etc.
I guess it’s easier to leave on a nice note but the temptation to whistleblow on all the sneaky, shitty behaviour that is going on it very strong.
What’s the most professional thing to do?

I think for your own sake it might be best to say you are looking for a new challenge, development opportunities, etc. Simply because the manager is friends with the inept team leader. The chances are that absolutely nothing will be done and sadly it might hamper your chances at getting the job.
But what might be more effective is if all the hard workers group together to make a complaint about the useless team leader. What you are describing is very unfair and wrong. Otherwise is there a HR department or another way to complain maybe anonymously?

No just say you want a new challenge!

Nope! Keep schtum and say new challenge - tempting as it maybe, no one comes off well with the dirty linen out in public.

After 3 more (hard workers leave) they might get the hint (but not likely ime)

I have worked in the same organisation for a long time (almost 20 years). Choose your words wisely. In my organisation, I have bumped into some of the same people along the way. Everyone knows everyone, and it doesn't take long for something someone said to get around.

I am leaving my current role for a number of reasons, including bad management and poor relationships with other agencies we are meant to work with (which is caused by bad management). I also cannot stand one of my co workers. It's a very stressful job (in part thanks to bad management) and I have simply said I want to do something less stressful. I think my supervisor knows my feelings on my colleague, but I haven't said anything about management. My new department is too close physically and organisationally for that IMO.

Id secure the new role first, then would tell all!

Talk about wanting the new challenges.

Anything you say is unlikely to result in action, it will just make you look bitter.

Besides there is a bloody good chance the boss already knows the culture is crap but as long as they manage to hit whatever targets he gives them he doesn't care much how they do it.

I wouldn't say anything negative about a former job at interview, even if you were applying somewhere else with a boss who isn't friends with your current boss!

Focus on the attractive things about working in the new team. Once you're safely out of the current situation (fingers crossed for you!) you could raise it with someone if you think it would be well received by management/not come back to bite you

Thanks all, just as I thought I will focus on the benefits of the new role when explaining why I’d like to leave to my current boss.

Our company is small and as much as I’d love to bare all there’s the risk that people move around and cross paths later on.

As you said it's a small world. I moved internally as I didn't like a few things my manager did - he was a poor manager. 8 years later he is still there and it is a small world and who knows where people end up.