There's not a vBulletin style daily digest of only subscribed threads. I can install an add-on that allows members to get an email daily containing ALL threads, but the forum is too big member-wise to use it really as we use Amazon SES to send mails and we'd get them throttled too much and / or start getting counted as spam.
A work-around that's perhaps a bit clunky is to create a folder in your email system and have our emails hit its own inbox, create a mail-rule to mark them all as read instantly, and then scan them daily or whatever.
I generally let gmail deal with it, it ends up in the 'social' tab along with dozens of other forums and rarely check the tab.
Another way perhaps is to disable email from thread subscriptions, and then just hit this page every couple of days:
http://www.electriciansforums.co.uk/watched/threads
Or disable thread subscriptions fully, and then just check your notices for replies. Again you'd have to come to the forum for that:
http://www.electriciansforums.co.uk/account/alerts
I did find the weekly / daily / instantly option handy on vBulletin forums to be honest. But it seems we're all about notifications these days and are assumed we either want emails about all actions, or none at all.