Cheapest ones he found I bet 
Get what you pay for
Coming from Yorkshire whilst I can be a tight arse on occasions I don't think this is the issue here. 
The problem here is the depth of part of the hub/disc shown in the photo bellow. I've not measured it but it is greater than 15mm which is why it is causing problems.
This is something which others have also experienced by the look of it.
http://www.golfgtiforum.co.uk/index.php?topic=164743.0
Would appear to be more an issue with the design of the mk3 rear hub than the spacers. I spoke to two companies before I bought these one of them Venom who said they don't supply 10mm hubcentric for the mk3 as they have had this issue, I just thought that 15mm would give enough clearance.
I know people do run 10mm spacers on the rear, ess three I know does, therefore I am assuming these must be the flat type.
Nope, mine are hubcentric.
Rear discs vary in the amount of metal on the spigot section...some hubcentric spacers fit, some don't.
My 10mm spacers are Eibach or H&R...and neither fit these discs, but they did the last ones I had fitted.
I filed off the upstand part of the 10mm spacer, so I kept the conical spigot locator, and use the spigot on the disc to locate the wheel.
This is the case on both the H&R and Eibach 10mm spacers...actually, if you tightened the wheel up it would shear off the offending bit, I just tidied up what was left with a file!
My 15mm spacers fit no problem IIRC.
The better way to do the job is to use rear beam spacers between the stub axle and beam, as this doesn't put higher load on the bearings.
I am running 10mm rear beam spacers...and currently 10mm wheel spacers too, until I've finished playing with tyre widths etc and I will most likely go with 20mm rear beam spacers.
