I have made some progress. I have the subform all set up as a continuous form.
I have a field in the form asin linked to the subform field asin.
When I click on a subform row the asin in the form updates.

The webbrowser is on the form.I have written the form as:

Private Sub Form_Current()
DoCmd.Maximize
If Not IsNull(ASIN) And ASIN <> "" Then
    'Webbrowser4.Navigate "http://www.amazon.co.uk/dp/B0146XE08Y" & ProductID
    WebBrowser1.Navigate "https://www.stockinthechannel.co.uk/Search?q=" & DLookup("MODEL", "AMANLISTINGS", " ASIN = " & "'" & [ASIN] & "'")
    
    'WebBrowser1.Navigate "https://www.stockinthechannel.co.uk/Search?q=" & DLookup("MODEL", "AMANLISTINGS", " ASIN = " & "'" & Forms![AMAZONDEALSF]![AMAZONDEALSUBF].Form![ASIN] & "'")
    
    'Forms![AMAZONDEALSUBF subform]![ASIN] Forms![AMAZONDEALSF]![AMAZONDEALSUBF].Form![ASIN]
Else
    WebBrowser1.Navigate "about:blank"
End If

End Sub

This successfully display the first item in the sub form.
When I go to the next item in the subform nopthing happens.
I tried setting up a refresh report on the form button but that just puts the subform selection back to the first item. So I cna upoadte the asin filed in the form but not the web control.
Please help.

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Reply from Alex Hedley:

Try adding some Debug.Print statements of MsgBox and see what ProductID is being shown