just found these in a drawer and as I no longer have my cz527 I don't need them they are 25mm
below is some bumpf I found on the cz site
Steel medium height scope rings are included with the CZ 527 M1 American that fit the 16MM dovetails that are integral to the receiver. The aft ring is keyed to lock into the receiver to prevent fore-aft movement. The medium height is to clear the ocular end of modern scopes. Inclusion of magazines and quality scope rings, I think, adds to pride of ownership. Rings are not included because they are hard to find. In checking discount retail I counted eighteen types readily available for the CZ 527.
from looking around at prices I think £20 posted is a fair price