Fortunately a metric circlip should fit,5/8 being .127mm under 16mm, a local bearing supplier, or fastener company should carry them. A quick search threw up this one: http://www.placeslocally.co.uk/bearings-stockists/essex/braintree/transmission-bearings-1362247.htm.

Tabulation of sizes attached, they are sized by the shaft they fit.

Sorry, yet another thing I knew about and hadn't passed on, purely one of those things that I have learned and forgot to tell you guys. Mine are always done, and it doesn't need lathe work.
 G'ville guys mostly bore the end of the shaft and thread for a bolt and large washer to go over the end of the shaft. That way if/when (and it's not unknown) the circlip departs the shaft won't wander out.

Thanks for the help and advice guys.
Stephen yes please, if you could bring it to Strettonthatwould be great.