Unusual Universal machine postmark.

Also in today's post was a letter from the London area.  I thought about putting this picture as a quiz question but I know that our readers are a knowledgeable bunch, so I'll save time and cut straight to the answer!

I haven't seen one of these used on new mail for many years, but at one time they were seen every October when the General Post Office conducted the mail census - machines counting the number of letters being processed through the sorting machines.  Once counted, this diamond postmark, usually without wavy lines, would be printed at the foot of the envelopes, the stamp having been cancelled in the usual way.

This was posted in north London, and I would normally expect a Jubilee mail centre postmark - either a packet or ink-jet.  Although this has a Large Letter stamp, that is from thickness: it's a 190 x 125 mm envelope so easily machineable.

I wonder what the circumstances were that not only could it not be put through the IMP or iSLM (whichever they have at Jubilee - I can never remember!), but they had a Universal machine operational and ready to use.  It can't have been the only mailpiece processed in this way: maybe it is a new procedure for dealing with skips, or uncancelled mail that would otherwise receive a pen cancel. 

We've been told that improved quality assurance would mean that Mail Centres would monitor cancellation as well as throughput: perhaps this is the answer?

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