How do I measure the return on my digital marketing?

You measure digital marketing by tracking enquiries back to their source, not by admiring traffic or follower counts. The number that matters is cost per enquiry: how much you spent to make the phone ring or the form submit. Set up call tracking and make sure your contact form records where the visitor came from, then compare each channel honestly. A channel bringing enquiries at £20 each is working, one at £200 each usually is not, unless your jobs are large. Check it monthly. Most Cornwall businesses find one or two channels do the heavy lifting and the rest can be trimmed. If your agency cannot show you cost per enquiry, that is the first thing to fix.