Mark Owen, South West Coast Path National Trail Officer, emailed to recommend his “best hike” in the world:
The South West Coast Path National Trail – 630 miles of superb coastal walking. From Minehead on the edge of the Exmoor National Park to the shores of Poole Harbour in Dorset it is the best way to enjoy the wonderful coastal scenery, wildlife and heritage.
He’s convinced us. We’ve added it to our list of the best hikes in Europe.
We love coast trails. The vistas are non-stop. Unless it gets foggy.
Of course you need not hike the whole thing. It’s very easy to section hike.
official website – South West Coast Path National Trail
besthike.com 
Ten years ago, I completed the small section of this around the “Lizard”, usually in 3 or 4 hour chunks. Fun, varied, and never far from a pub!
The south west path is fantastic, great addition to the lost. However, if you’re going to add the Cornish Coast to your list, you really should consider the UK’s other great long distance coastal path, the Pembrokeshire Coast Trail in south Wales – the scenery is relatively similar, but being mostly within the Pembrokeshire Coast National Park is less developed, less touristy, a bit more rugged (and a bit wetter) – and overall I reckon a bit better. It’s also one of the best places in the country to see seabirds, too. I’ve only done sections, but the bits I have seen are stunning.
Here’s the official site:
http://nt.pcnpa.org.uk/website/sitefiles/nt_page.asp?PageID=2
& here’s someone’s account of their trip:
http://www.gtleisure.co.uk/walks/pc01/pembcsta.htm