The rehabilitation act regarding the spent period is based on the sentence given by the court, ie. community service, custodial etc, not on the offence itself. Any prison sentence over 10 years can never been spent so will remain on your record for ever, however it would be a mean judge to award you that for common assault. (saying that I believe the maximum sentence for common assault is 6 months)..
Look up your sentence given not served against the chart and you will see how long it lasts. By the time you get a job it will be well spent anyway
