Serial number is 8964
I am unconvinced that it is 80's for the following reasons:
built for 27 x 1 1/4 wheels
brass grease nipple in bottom bracket
braze ons for over bb cable routing
Rake of the fork - looks much closer to the french/ jack taylor style which they changed to the very slight rake more familiar to mercians
Here is an example from 89, where you can see things like
canti mounts,
a tubular rear cable hanger (mine is a shaped plate),
multiple mounting points for panniers etc, engraved seatstay caps,
TT cablerouting is different
shallow fork rake,
brazed shifter bosses
https://www.retrobike.co.uk/threads/mercian-king-of-mercia-touring-bike-60cm-1989.324366/
RE price:
I bought it for £300 as pictured but I made the mistake of doing so in the dark when I couldn't tell ho bad the coading was. As soon as i tested it I could tell it was an excellent bike.
@Suffolk roads The fact that you say that makes me think I shouldn't.... Like I say Im in no hurry to sell. Could I be cheeky and ask what you think it's worth?