I was preparing for my first year progression review and was trying to find a paper I had seen for my literature review. In looking I stumbled across a term that I had not checked before in my literature searches which lead me to a significant number of sources who had done roughly what I had done and had thought had been unique. What do I do and how do I tell my supervisor? My review is in a week. I had always maintained in meetings that I had been unable to find sources doing what I had done but that I wasn't 100% sure that I had not missed something.

Don't worry. In all likelihood, yours is different somehow (and thus has some originality). Read the paper carefully, see how yours differs, and maybe have a go at coming up with some ideas about how you will take the project forward - perhaps in a slightly different direction than first envisaged. Your supervisor should be able to help with this too (it could be discussed in your progression review). To be honest, this kind of thing happens. I think the main thing is to see how yours differs (did you get the same results? use the same methodology? same measures etc?) and to make the plan going forward...

It's better to find this out now than a month before submission. These things happen and you're early enough in the process to be able to tweak things. I'd tell your supervisor right away - s/he will be able to reassure you. Ask your supervisor for advice about how to address this in your review meeting but I wouldn't worry about amending documentation etc.

Honestly, in the first year this is not a big issue. You have plenty of time to sort it, make changes or whatever you need to. Better to have found this out now than at your viva.

This is ok...reach out to those authors and share your passion for what you want to do and then ask them how to tweak the work in an interesting angle, you will be amazed!