UK VAT Supplier (Tax Registration Number)

I wonder if anyone can help with this query. I have followed
the guidance in MOS note 1080383.1 and am still confused. Here is my example.
Try to set up supplier with Tax Reg number 947405801. This should work as
follows:

 

9x8=72

4x7=28

7x6=42

4x5=20

0x4=0

5x3=15

8x2=16

Sum = 193

 

Less 97 = 96

 

96-97 = -01

Therefore check digits (8&9) are 01

 

This should allow input but gives me the error:

 

“Please enter a valid tax registration number”

 

Even more strangely if I prefix with GB ie GB947405801 it
does allow me to carry on with the input!

 

Can anyone help?

 

Thanks, David