Incrémater une donnée alphanumérique sur la premiere cellule vide

Sub Incrementer()
Dim t$, i%
With ActiveSheet.UsedRange
    .Sort .Columns(1), xlAscending, Header:=xlYes 'tri croissant sur la 1ère colonne
    With .Cells(1).CurrentRegion
        With .Cells(.Rows.Count, 1)
            t = .Value
            For i = 1 To Len(t)
                If Not IsNumeric(Mid(t, i, 1)) Then Exit For
            Next
            .Offset(1) = Format(Val(t) + 1, String(i - 1, 0)) & Mid(t, i)
        End With
    End With
End With
End Sub