I see both sides of the coin.
On the one hand, one car that you know and have developed a relationship with can be very handy at both ends of the journey. And it is much less hassle than fueling and turning in and hiring two different cars.
On the other hand, what "flexibility" do you want? Are you intending to stop at Little Moreton Hall or Biddulph Grange, or will you just grit your teeth, roll up your sleeves and plunge into the horrible experience that the M6 is, with all the other fun motorways, all the way from Kingham to Kendal? If you do choose to drive, I'd expect Fosseway from Stow-on-the-Wold or Moreton in Marsh up to the M40, then M42 north to the M6 Toll (get a bank loan) to M6 or M42 west to M5 to M6; then M6 all the way to Kendal.
The M6 is simply a disaster and horrible to drive. When you reach one of the many construction areas (where they are slowly slowly installing what the government optimistically calls "Smart Motorway" which is fancy way of saying remove the hard shoulder for all liane running and install variable speed gantries to issue tickets) you must reduce whatever speed you have to the posted road works speed which is STRICTLY enforced by those cute yellow poles which have speed averaging cameras. Most places it is down to 50 mph, but several now are 40. Don't get upset when heavy trucks pass you - they seem invulnerable. The tickets are high. And there is heavy traffic on the entire journey once you are off the M40.
So it really is personal preference.....