Sven,

You've hit on one of the major inconsistencies of British/European signage. No left/right/U-turn signs show the symbol crossed through with a slash, but other prohibition signs don't. Crazy! Britain started adopting these Continental-style signs in the mid-1960s.

(By the way, whereas U.S. versions of no xx-turn signs are on a square white background, ours are actually circular signs.)

Oh yes... And here's the sign for a cycle route:

[Linked Image from highwaycode.gov.uk]

Clear as mud now? [Linked Image]