I tried to recall, but I guess the OP is right, I cannot remember getting a clearance "as number x" in the UK - never really thought of it. In other parts of the world I remember a lot of instances like "cleared to land as number two after Mooney ahead turning base, report traffic in sight" or "cleared to land purple, on the numbers, as number six".
Reflecting this, I came across a similar topic: if you receive a "continue approach as number two" VFR in controlled space and number one receives clearance to land, when do you turn base?