The Vacant Property Refurbishment Grant requires the property to have been vacant for a continuous period of at least two years immediately before you apply, and you must evidence that vacancy to the local authority.
Local authorities look for objective evidence covering the whole vacancy period rather than a statement from the owner. Utility account records showing negligible consumption are the most common proof, supported by the authority's own inspection.
Short lettings or occasional occupation during the period can break continuity, so gather the records before applying rather than after.