I read somewhere, think Benefits and Work, about the 21/2 centimetre coin or less argument-that is picking up a coin doesn't fail the test because there are smaller coins to test the claimant. Tried it at appeal and Tribunal didn't like it but I came across this in TC Guidance section about disabilities that put you at disadvantage of getting a job.

http://www.inlandrevenue.gov.uk/manuals/tctmanual/TCTM02505.htm#4