Sql stored procedure returning syntax error when using conditional where clause

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SQL-Server-2014

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I have the following stored procedure which takes 2 parameters. The @Class parameter can have any one of 11 values. Depending on the value the where clause looks at a different column.

The procedure compiles ok and if I copy the print and paste it into a new query window it runs fine, but if I execute the procedure I am getting an Incorrect syntax error message near 'Bristol' but cannot figure out what I need to do to fix despite looking on here and on other web pages. Any help would be much appreciated

What I have tried:

    ALTER PROCEDURE [TTR_HazDriver]
	@Depot nvarchar(50),
	@Class nvarchar(1)

    AS
    BEGIN
	DECLARE @Where nvarchar(1000)
	DECLARE @sSql nvarchar(MAX)
	DECLARE @Order nvarchar(1000)

    SET @sSql = '
    SELECT EM.EmployeeNumber
    , EM.EmployeeSurname
    , EM.EmployeeInitials
    , D.Depot
    , EDL.Class1
    , EDL.Class2
    , EDL.Class3
    , EDL.Class4
    , EDL.Class5
    , EDL.Class6
    , EDL.Class7
    , EDL.Class8
    , EDL.Class9
    , CONVERT(VARCHAR(10),EDL.ExpiryDate, 103) ExpiryDate
    , EDL.Tanks
    , EDL.Package
    FROM   EmployeeMaster EM 
    LEFT OUTER JOIN PayrollFrequency PF ON EM.FrequencyDesc = PF.DescCode 
    INNER JOIN EmployeeDrivingLicence EDL ON EM.EmpCode = EDL.EmpCode 
    LEFT OUTER JOIN Depot D ON EM.Depot = D.DescCode'

    SET @Where = '
    WHERE (D.Depot = ''' + @Depot + ''' OR ''' + @Depot + ''' IS NULL)
    AND EM.EmployeeLeft = ''N''
    AND PF.FrequencyDesc = ''Weekly'''
 


    SET @Order = '
		ORDER BY D.DepotDepotDescription
		, EDL.ExpiryDate'
 
    IF @Class = '1' 
	SET @Where = @Where + ' AND EDL.Class1 = ''Y'''
    IF @Class = '2' 
	SET @Where = @Where + ' AND EDL.Class2 = ''Y'''
    IF @Class = '3' 
	SET @Where = @Where + ' AND EDL.Class3 = ''Y'''
    IF @Class = '4' 
	SET @Where = @Where + ' AND EDL.Class4 = ''Y'''
    IF @Class = '5' 
	SET @Where = @Where + ' AND EDL.Class5 = ''Y'''
    IF @Class = '6' 
	SET @Where = @Where + ' AND EDL.Class6 = ''Y'''
    IF @Class = '7' 
	SET @Where = @Where + ' AND EDL.Class7 = ''Y'''
    IF @Class = '8' 
	SET @Where = @Where + ' AND EDL.Class8 = ''Y'''
    IF @Class = '9' 
	SET @Where = @Where + ' AND EDL.Class9 = ''Y'''
    IF @Class = 'T' 
	SET @Where = @Where + ' AND EDL.Tanks = ''Y'''
    IF @Class = 'P' 
	SET @Where = @Where + ' AND EDL.Package = ''Y'''


    SET @sSql = @sSql + @Where + @Order
    PRINT @sSql
 
    EXEC sp_executesql @sSQL, @Depot, @Class
    END

The print statement produces the following query:

    SELECT EM.EmployeeNumber
     , EM.EmployeeSurname
     , EM.EmployeeInitials
     , D.Depot
     , EDL.Class1
     , EDL.Class2
     , EDL.Class3
     , EDL.Class4
     , EDL.Class5
     , EDL.Class6
     , EDL.Class7
     , EDL.Class8
     , EDL.Class9
     , CONVERT(VARCHAR(10),EDL.ExpiryDate, 103) ExpiryDate
     , EDL.Tanks
     , EDL.Package
     FROM   EmployeeMaster EM 
     LEFT OUTER JOIN PayrollFrequency PF ON EM.FrequencyDesc = PF.DescCode 
     INNER JOIN EmployeeDrivingLicence EDL ON EM.EmpCode = EDL.EmpCode 
     LEFT OUTER JOIN Depot D ON EM.DepotDepotDescription = D.DescCode
     WHERE (D.DepotDepotDescription = 'Bristol' OR 'Bristol' IS NULL)
     AND PF.FrequencyDesc = 'Weekly'
     AND EDL.Class3 = 'Y'
		ORDER BY D.Depot
		, EDL.ExpiryDate