HOW MUCH?

A Guernsey 20p piece which I found underfoot in a muddy car park about a week ago. I wasn't sure about the design* so I looked it up on a couple of coin sites, found it was said to be worth maybe £2 in good condition although one supreme optimist was asking for £340 on a collectors' site. This one has obviously been well-used and can only be worth 20p but I'm putting it to one side because my Dad was born in Guernsey and I believe that his father was as well.

*I think that Her late Majesty looks in a pretty grim mood.