I'm way out of my comfort zone when it comes to British stuff, although I grew up riding dad's old bike, which I believe was a British machine with 50's Campagnolo parts and I distinctly remember the fancy lugs and GB stem. He sold the Campagnolo to the joiner down the road in the 70's, so I know that's no longer with us.
It's still in the garage loft and I'll have to dig it out as it's piled under tons of....., well you know, there's tons of it anyway.
I'm there next week and I'll take some photos if I can get to it.
Anyway back to this Mercian, I had a look around t'internet and couldn't seem to come across this particular style of Mercian frame decal, but I did see somewhere that the script style changed to Gothic in the early 60's. I thought the head badge was particularly interesting too as they have a modern take on it here;http://lovelybike.blogspot.co.uk/search/label/mercian
Not as nice as the original though...
Is that the world championship colours along with the Olympic rings? and what does this signify or which Olympics does this relate too ?