CRB and Convictions - From Anon

21 years ago I did something stupid and ended up in prison for theft. I only did that 1 sentence and never ever offended again. I have a wife and three children and have been a builder all my life. Work has dried up and I have been unemployed now for 7 months. I wanted to try a new career in the healthcare sector and have been for roughly 7 interviews and failed on all 7. My conviction must show on my CRB and on every interview I have been honest and up front with the interviewer. But I just can't get there and get a job. Will it show up after 21 years on a CRB does anyone know? This is what I am thinking and that's why I can't get a job? Any help welcome. Thanks.