Thunderbug,
sorry old boy, you are wrong, ALL convictions, spent or not, have to be declared on the form
As you rightly say, the result of the CRC will return spent convictions and if you haven't declared them when asked to do so, the employer will rightly wonder what else you have to hide.
Jeffrey,
Despite the above, I wouldn't worry, declare whatever you are required to and be open and honest if asked.
Do the right thing but bear in mind is that a blood test may be required for the medical - this will definately show up any recent daliences with anything naughty.