Planning permission is typically not required for installing French doors, as it often falls under "permitted development rights" for homeowners. However, there are certain situations where you might need planning permission:
If your property is a listed building, you'll likely need listed building consent.
If your home is in a conservation area, national park, or Area of Outstanding Natural Beauty, there may be additional restrictions.
If your property has had its permitted development rights removed or altered via a planning condition or Article 4 Direction, you may need to apply for planning permission.
If the French doors will be facing a public highway and are less than two meters from the boundary, it may require planning permission.
To be certain whether you need permission for your specific situation, it's best to consult your local planning authority (LPA). They can provide accurate and up-to-date information on building regulations in your area, so you can make an informed decision on whether to install a set of double french doors.