A few days ago after the appalling attack in Manchester, James Heappey wrote me a campaign email:
"Campaigning resumes at midday today after pausing for a few days to reflect on the horrendous attack in Manchester. The tone of the campaign ... will hopefully continue to be respectful over the next week" [my emphasis]
So where does “Why don't you fuck off back to Scotland?” fit into that plan?
When meeting the sixth form at Millfield school in Street, Somerset, Heappey asked pupils how they would vote in the proposed second Scottish independence referendum. A Scottish girl said she would support independence. Most reports assert that Heappey then asked her "Why don’t you fuck off back to Scotland?"
A good starting point to read the many reports is Heappey's page on Wikipedia.