Lovely frame, but not a Cinelli.

I think this is a 1975 Witcomb (of London). The last 2 digits of the serial number indicate the year:





Witcomb did custom frames and customers could choose whatever they wanted on a frame. They also had a number of builders over the years, so there's a wide range of styles that you'll find on their frames.
I've seen most of the features of this frame on other Witcomb bikes, although some not very often. The stay caps and the circular cutouts in the lugs were not common. The Milremo crown (or whoever produced that one for them), the cable stop/guide combo and the brazeon on the underside of the down tube were more common.

Here are some pics of the less common features:

Circular lug cutouts:





Similar seat stay cap treatment:




There are more pics of serial numbers and other bits on a couple of other Witcomb thread:

Have I got a Falcon?
A mysterious braze-on


Finally, I'm not sure when JP Weigle left Witcomb in Deptford and started at Witcomb USA, but you can find this frame on his flickr page. It has (somewhat) similar seat stay caps and the circular cutouts on the head lugs - it'd be pretty special if he was involved in build of your frame: