Here is a summary of traveling to your Gastrobiking holiday.
Grenoble Airport : Ryanair from Stansted.
Lyon St.Exupery : Easyjet from Stansted, BA from Heathrow, Manchester and Birmingham.
Paris Charles de Gaulle : There are many flights and there is a direct TGV train from the airport to Valence station (2hrs). This is not only easy for outside Europe but also from the UK and Ireland.
Valence TGV is only 30km (20 miles) away and has a direct service from Paris. From London you can change at Lille, thus avoiding Paris, for a journey time of 6 hours. Fares from £99 return.
There is motorway to within 5 minutes of St.Nazaire-en-Royans so it's an easy drive. From the UK, Speedferries provide a cheap, fast and comfortable Channel crossing. Driving time is approximately 8 to 10 hours.
The European Bike Express is a coach service from the North of England which drops you off at Valence. Your bike is stored in a custom built bike trailer.