Criminal spent/unspent convictions

TBagpuss

Based on what your record shows, you were given a 12 months custodial sentence, suspended for 24 months.

According to this table https://www.gov.uk/guidance/rehabilitation-periods, this means that this counts as a custodial sentence of more than 6 months but under 2 1/2 years, so is is spent 4 years after the sentence is completed.
So if you were convicted in January 2018, the 12 month sentence is completed in January 2019 and would be 'spent' 4 years after that, in January 2023.

At this point, when the check is done the conviction will show up so as far as the employer is concerned, you lied on the application, and lied about having convictions for an extremely relevant offence. 
 
Your best bet may be to contact them to let them know you made a mistake and ask if you can correct the error, but it may be too late as it is likely to look as though you only gave them the information when you were made aware that it would be checked. but I would suggest you contact Nacro (https://www.nacro.org.uk/) who can offer you advice and help.