Combining two columns in a table into one ordered list

Thanks all, many options to consider and working perfectly

another option without LAMBDA function:

=LET(pp,TRANSPOSE(UNIQUE(project)),
     TOCOL(VSTACK(pp,IF(pp=project,detail,NA())),3,1))

Looks like an opportunity to use PeterBartholomew1 's MAPλ

=MAPλ(UNIQUE(project), LAMBDA(v, VSTACK(v, FILTER(detail, project = v))))

Thank you for the contribution, this may be a full back option but my workplace is very strict on Macros. 

Therefore the formula either LET/LAMBDA would be the preferred option if someone is able to advise

Thanks

Matt

Nice challenge for a lambda function, but too complicated for me. Here is a VBA user-defined function that returns what you need:

Function StackTableBy1stColumn(proj, detail)
    Dim i As Long
    Dim res As String
    Dim projData As Variant
    Dim detData As Variant
    projData = proj.Value
    detData = detail.Value
    For i = LBound(projData, 1) To UBound(projData, 1)
        If i = 1 Then
            res = projData(1, 1) & vbNewLine & detData(1, 1)
        ElseIf projData(i, 1) <> projData(i - 1, 1) Then
            res = res & vbNewLine & projData(i, 1) & vbNewLine & detData(i, 1)
        Else
            res = res & vbNewLine & detData(i, 1)

        End If
    Next
    StackTableBy1stColumn = Application.Transpose(Split(res, vbNewLine))
End Function