I just tried switching to the new (google) version of Blogger. It didn't work though. According to the help notes it could be because the blog is too big. I am advised to have another try later.
I am slightly concerned it might wreck my blog as I have fiddled with the code a bit over the years. I am not an IT expert and I really don't want to lose my entire blog and have to start again...! Any advice is welcome.