I've done my fair share of hiring (Tech company in London), and I don't think I've ever seen a cover letter included with any CV. Recruiters either don't ask for them or don't bother to pass them on. When we get referrals from our colleagues, it's typical just to ask for a CV and get a phone interview set up as quickly as possible. Maybe it's different if you do a lot of direct hiring.
I believe most recruiters would prefer they write the "cover letter". All it's meant to do is highlight what parts of your resume make you a great fit for the job.
Typically emails you get will look like "Hey ucosty, we've got some great candidates for you. I've attached their CVs here.". For emails from referrals they're more likely to be "Hey ucosty, your colleague foobar referred me. I've attached my CV"
