Yes, you can be denied a job. You can look in to sealing your record but with all the private websites like mugshots.com out there, your arrest will probably be found. You are correct in telling employers that you have never been convicted. you may wish to disclose the arrest with an explanation that the charge was dismissed.
Yes you can legally be denied a job. If you successfully completed the terms and conditions of the deferred prosecution and the charge was dismissed, speak to an experienced criminal defense attorney about an expunction.
I would seek to get the charge expunged. You may be eligible. See http://www.minicklaw.com/tag/expungement/ for more info.
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