Writ 66 is just one of a number of downloadable forms, so what makes a genuine writ? Civil Rules Part 83 appears to deal with this matter.
It speaks of three documents. The judgement, the request and the writ.
So, if I have it right, there will be the original judgement. This is what bears the judge's signature and it is only this that bears the judge's signature.
There is then a request for a writ which must be signed by the creditor or their solicitors, and the judgement or an office copy of the judgement must be presented to the clerk.
On payment of the fee the clerk will then issue and seal an actual writ. There will be one original copy of the sealed writ which has to have the correct date of sealing on it.
Additionally from a FoI request there is the following helpful extract:
(My highlighting)In neither the Civil nor Family jurisdictions is there a prescribed form for the seal.
CPR r.2.6 and FPR r29.7 state that the court may place the seal on the document by hand; or by printing a facsimile of the seal on the document whether electronically or otherwise. There is therefore no requirement for an embossed seal; a print of the court seal could (and usually will) be integral in the word-processed order or by way of a rubber stamp.
Additionally the FoI helpfully points out that button seals are only applicable to High Court judgements.
In conclusion, the numpty only needs to look at the top right corner to see the official seal. It's the big circular stamp!
Addendum
Found this:
Where sealing or signature is required, failure to seal the order would have no effect on the legality or effect of the court order. The legality and effect of the order is created by the announcement of the judge, magistrate or justices’ legal
adviser, not by a court officer committing it to paper. The primary effect of sealing is to authenticate the order so that it is admissible in evidence or in other proceedings, for example foreign enforcement.