Looking at the image below, you see that the distance between each "200 yard" sign is actually 200m, so this means that the signs are obviously inaccurate. What's stupid is that the DfT mandates that signs be placed in distances that are specified in metric units (usually m or mm), however the content of the sign is imperial, and therefore innacurate! 200m is 218.72 yards, therefore, why not just write 200m on the signs?
If people don't understand the metre, let them learn!
We really don't need to 'dumb down' metric units for people, or there'll never be any progress in relation to full metrication! The best way to learn something is by full immersion.
(image taken from the UKMA website)