Posts page not working

Hi

I am developing my wordpress website locally and I am in the process of tweaking my theme.

I have set a static home page which is working fine. However, when I try to set a page for posts it appears to use single.php instead of index.php. I have no idea why this is happening.

Does anyone have any suggestions on how to fix this issue?

PS. I have tried deactivating all plugins and it made no difference.

Thanks