You should be able to find tariffs here @Emmywoo 

https://plans.ovoenergy.com/
If you untick Available for sale, you should see historic versions too. 
It’s difficult because tariffs are area related. 

Thanks for the info. It doesn't appear to have the tariff I'm looking for, for the period I'm interested in. 

Not sure how else to check.

I found this in the forum from earlier this year - might help. In particular, look towards the end and Firedog’s figures 

Thanks for that, apologies if you've gone to effort looking for that. I'm not entirely sure how to search through the forum.

The prices are the price cap, but they are useful in that I know roughly where the ones I've been charged fit. I'll just see what ovo say about it when I query them.