Sorry, I have been unable to get to my computer for a few days.
Reverting to this issue, thank you Alex and Mubeezi for your helpful comments.
So far as Mubeezi's comments are concerned I have changed the "reserved word" description to detail which is supposed not to be reserved, although it does conflict with the name for the area where the fields are inserted which I have had to change to "details".
Otherwise the suggestions do not work.
So far as Alex' comments are concerned I have indeed tried it in a query where I get
WHERE Detail Like "*" & [Enter Detail] & "*"
This I incorporate into my "after update" vba as follows:
    Dim W As String
    Dim R As String
    Dim S As String
    
    
    W = ""
    S = " * "
    
    If Not IsNull(DetailFilter) Then
        W = "Detail Like " & S & DetailFilter & S
    
    End If
    
But it does not work.  When I enter a string, such as "abcd" for which I wish to search into the text box I get the following message when I move away from the text box:
Run-time error '3075'
Syntax error (missing operator) in query expression 'Details Like * abcd *'.
If I click on debug i get to the line:
    Me.RecordSource = R

Clearly I have gone wrong somewhere, but cannot work out where.

Any assistance would be gratefully received.