Thanks Robbe, I tried that, and found this method works:
Application.DisplayAlerts = False
Selection.GoTo What:=wdGoToBookmark, Name:="Text1"
With ActiveDocument.Bookmarks
.DefaultSorting = wdSortByName
.ShowHidden = False
End With
Selection.LanguageID = wdEnglishUK
Selection.NoProofing = False
Application.CheckLanguage = True
If Options.CheckGrammarWithSpelling = True Then
ActiveDocument.CheckGrammar
Else
ActiveDocument.CheckSpelling
End If
Application.DisplayAlerts = True
It seems to be the line ActiveDocument.CheckSpelling that is required. As I only want one particular form field checked, turning off display alerts stops the prompt for checking the rest of the document. Oddly, if I change that to Selection.Range.CheckSpelling it ONLY checks the grammar. Not sure why, but at least I have a solution.