Hi Richy
I believe there is every likelihood that your conviction would be eligible for filtering provided that you only have one conviction and one charge.
If you've still got the CRB certificate that you got in 2011, you might want to have a look to see what section of the Theft Act you were charged under. Providing it's not one of the following, then it will be eligible for filtering.
Theft Act 1968, S10
Theft Act 1968, S12A
Theft Act 1968, S8
Theft Act 1968, S9(1)(a)
Theft Act 1968, S9(1)(b)
If you haven't got your old CRB and you really want to be sure about this, then your best bet would be to get a copy of your police record (a Subject Access Request) - details of how you go about this can be found at -
https://www.acro.police.uk/.
Assuming that it will be filtered, then it won't appear on your DBS check (the new name for a CRB) and you won't need to disclose it to any future employer.
Hope this helps but feel free to contact the helpline if you need anything further.
Good luck
Debs