Found - float line in waist bag. Probably belongs to an instructor taking group up the waterfalls in upper River Esk. To return email me with colour and make and we can arrange to get it back to you.

I know that the instructors from The Kepplewray Centre in Broughton run regular trips up the Esk, maybe get in touch with them if you don't get any luck?

Cheers.  I've emailed them.