<<I've replaced the blown 15A fuse on the blue (rearmost) relay with a 30A fuse and the fans now run properly - a minute or so after the A/C is switched on.
The Green relay - high speed/high temp - has a functioning 15A fuse which I will replace tomorrow with a 25A as you suggest.>>
I don't have wiring diag. for UK spec cars , but all US version 104 engs relay layouts show the blue relay to go in slot "C" [foward]
This is relay K9/high speed -eng temp activated.
The green relay is the low speed [a/c high pressure activated] and it's posistion is slot "B" [ rearward]. This is relay K10.
If the wiring is the same as US versions , I believe someone has switched the relay locations and that is why you have had fuse failures...
If you find this to be the case , then you want the posistions as stated and want a 30A in the green relay , in the rear slot,,,, and the blue relay in the foward slot with a 25 A fuse....