Great Britain. Is This A Pre-Cancel?

The stamp still has gum. Appears to be, never used.

I wouldn't call it a pre-cancel. It's one of those security things (like perfins) to stop the stamps being stolen and used. The overprint doesn't cancel the stamp, it tags it as property of John Barker Co Ltd.

For legal or other use where a document had to be stamped, perhaps, given the "received by" text.

I would call it an 'overprint'

Just as the stamp states, postage / Revenue. Great Britain step were used for both postage & fiscal use and this one has a private print as mentioned, intended for fiscal use which in many collectors worlds decreases the value.

Of course. It's a private company overprint not a precancel. I wonder did the company do the overprinting? Or did the postal agency do it upon order?

This is a commerical overprint used for thift control and/or commerical revenue in Great Britian. Please check out the site www.cosgb.org !

Until about 1970 every receipt issued in the UK, in order to be valid, had to have a stamp attached to it. This was a form of taxation - a halfpenny for small sums, more for others. To ensure the stamp could not be taken off the receipt and used for postage (which would be a loss of revenue to the Post Office) the person issuing the stamp had to sign across it in ink, to invalidate it for postal use.

Many companies added an overprint, firstly to ensure that it was invalidated for postage even if someone forgot to sign it or tried to 'wash' it, secondly (as suggested above) to prevent in-house pilfering and thirdly to reduce the chance of someone faking a receipt by forging a signature on an ordinary stamp and claiming this was evidence they had made a payment.

Great info, thanks!