There was an interesting interview with a relevant scientist on R4 this afternoon. He said that the air in even old-fashioned aircraft is changed very frequently and that transmission of virus along the length of a plane is unlikely, because of the direction of air flow in the air exchange system. He said that the person you are most at risk from is someone sitting next to you or a sneeze from the person in the row behind - but presumably if proper social distancing is in place, there simply should not be someone sitting in the row behind.
It would make sense for people from the same family to be seated together in their bubble; and the next bubble to be seated further away; rather than individual spacing.
But, having said all that, I see no reason to take that risk at present. Lots of beautiful places in UK that could be visited in one's own car and in self-catering accommodation.