Sounds like an awesome week of training to be had that!
Sure be some good flights for you from London but this is potentially on my radar from the skyrunning world series
Looks seriously epic terrain with quality mountains and a nice wee place to visit. If the timing was not great certainly use the race route for area inspiration.
Other safe bets would include Chamonix or Annecy area, and then also heading down to Sierra Nevada south spain or Finnestrat area to the east near Pennysogolosa etc.
I am planning Kima for end August in the Val Masino area of Italy so this area could also be quality, which remind me, the Aosta Valley also in Italy well worth a visit!
Almost overwhelmed with choice here as a start to type…. hahaha. Hope that helps a bit!