I uploaded .jpg screenshots of .pdf statement downloads (Royal Bank of Scotland & Nationwide) for our applications and they were granted without any problems. Mine came through in 3 days, wifes took a week, possibly due to being born in Thailand and having changed her name (didn't use her Thai passport due to having no vaccination record against her Thai name).
The online application pages are somewhat confusing as to whether .pdf or .jpg is needed, I just tried one and if it wouldn't upload tried the other format.
Andrew