Is it legal to avoid the UK quarantine (August 2020) on passengers returning from France by traveling via another country?

I'm British, due to travel to the south of France for a week, flying from London to Turin (Italy) and driving across the border (it's the closest airport to my destination in France)

The UK has just (14 Aug) brought in travel restrictions requiring travelers from France to self-isolate.

Technically I will have 'traveled from Italy' when I return. From what I've read, I think this means that under UK rules I'm not legally obliged to self isolate on return.

Is this correct?

I'd like to cancel my trip, but this is further complicated my COVID-19 travel insurance refusing to refund anything because travel to/from Italy is not affected by the new restrictions.