I went first to Steve Morse's One-Step Web pages. This is the page for searching Ancestry:
http://stevemorse.org/census/uk.html
I chose 'England' 'Buckinghamshire' from the drop-down lists and entered 'Gawcott' in the box marked 'town'.
Since I don't have a World membership there (I'm in the US), Ancestry returned a list of 400 names in alphabetical order. I can see the county people were born in but not their residence or their parents / spouse names.
E.g.
Anne M S Abbotts name abt 1876 city, Buckinghamshire, England relation city, Buckinghamshire
'name' 'city' 'relation' are links which take the user to the 'don't you want to sign up for a subscription now' page.
However, had I been able to view an individual record, that would have given me some idea of what the ED might be.
For 1901censusonline, the link is:
http://stevemorse.org/census/uk1901a.html
I repeated the search, but for that site, you cannot search for the entire town. You must search for at least part of a name (little boxes pop up to advise you which searches are possible and which are not).
Next I checked World Vital Records, which makes available some census data from FindMyPast.com (though not 1901).
It's possible there to simply search for 'Gawcott' in the place field and then see what happens. I got 995 hits, many of which were people who were born in Gawcott, addresses of Gawcott Road, and so forth -- the search result pages show the Registration district rather than the town, so not much help there.
Searching the gazetteer on 'A Vision of Britain Through Time' got this result in the Gazeteer:
http://www.visionofbritain.org.uk/
Associated administrative units:
Unit name Type of unit
Buckingham AP/CP Parish-level Unit
Buckinghamshire Ancient County
I would say next time start at 'Vision' -- if the plain place search on the main page yields no results, try the gazetteers next. That would allow you to get to the likely civil parish without guessing. From there Genuki might be able to tell you what the equivalent CP was for the census you are searching.
(I can't say how long the search took, because I was writing the message as I was going along, which was more time-consuming than the search itself.)
Hope this helps.
Jan