To Toulouse, then a drive of 90 minutes to Clement La Baste. Easyjet fly from Gatwick and Bristol to Toulouse — both very reasonable. British Airways also fly to Toulouse..
Eurostar to Agen or Toulouse — 5 hours from Paris.
From Calais, Clement La Baste is 644 miles with a driving time of approximately 12 hours.
Whichever way you decide to travel, a car is advisable to appreciate the area.