Many thanks for your patience. The first issue is that you have no proof any breaches of confidentiality were made and you are speculating. The timing may be suspicious but that does not mean it is because of what you think happened. Some proof will be needed.
Secondly, you were not guaranteed this job – you had only applies for it and were waiting for the decision. You were not offered it and then had the offer withdrawn. So there is no guarantee you would have got the job even the was no issue with the disciplinary. You have to remember that an employer can choose whoever they want for the job, even if they are not the best and they can decide to refuse to employ the best candidate.
Finally, there may not have been a breach in the first place. For example, your personnel file could be accessible by anyone in the company who has the authority to do so, such as managers. The department you were interviewing for could have simply exercised its access privileges to check your record. That is not a breach of data protection – these people could have had the right to access it in the circumstances.
It is also worth mentioning that the most appropriate remedy here would have been of constructive dismissal but you need to have 2 years service to be able to claim which you do not have. So whilst you can complain internally to the employer about this, and is impossible for you to make the usual claim in this situation and anything else is going to be rather difficult to pursue. So use the grievance route but consider leaving it at that as it is unrealistic you can do anything else about it.
I hope this has answered your query. I would be grateful if you could please take a second to leave a positive rating (3, 4 or 5 stars) as that is an important part of our process and recognises the time I have spent assisting you. If you need me to clarify anything before you go - please get back to me on here and I will assist further as best as I can. Thank you