I'm from Oxford (I was born there) and I'm not surprised at all that people there have very little time for Trump. I'm glad the shopkeepers were able to commiserate with you.
Anyway, yes - You've Been Trumped made me really angry (in a good way). It also celebrates the spirit of the little guy against bullies like Trump, and his unholy alliance with the Scottish nationalists. Not to mention the various other shamefully corrupt people who colluded with him by their repeated attempts at bullying people off their land for that wretched golf course. My father was a Scotsman (he was born in Fort William) but he was an ardent unionist and detested the Scottish nationalists. With this film, I could start to see why.
And yes, good for David Tennant. :)
Speaking of King Arthur, there's a ton of Arthurian mythology and locations here in southwest England (where I live these days). :)