With some polls suggesting a slim majority of people in Scotland now support independence from the rest of the United Kingdom, Johnson was keen to press the case for the whole country working together to tackle the coronavirus and its economic impact.
The pandemic and Brexit have badly strained the ties that bind the kingdom's constituent parts - England, Scotland, Wales and Northern Ireland.
Scotland's pro-independence government opposes leaving the European Union and accuses Johnson of mistakes in responding to COVID-19.
Scotland voted in 2014 to remain part of the United Kingdom, but polling shows it remains deeply split over the issue.
Johnson said on Thursday (July 23) that the union was a "fantastically strong institution" and that the 2014 vote should be considered the "once in a generation" event it was described as at the time.