Admittedly, I cannot see any satisfactory solution to this problem Nor anyone,so far, whom I have approached on the subject, so I don't expect to be inundated with reples ! but anyway here goes.
Our conservatory over loooks a particularly beautiful south facing view. ( No that's not the prob ! ) We will be having new wooden double glazed doors. The present single glazed doors open outwards but unfortunately cannot open right back against the walls due to a rather wide slate window ledge and beneath this the base of the conservatory is made of large raised stone work . The only possible idea so far is to have the new doors fitted to extra long parliament hinges.( which will need to be custom made ) but these will jut out somewhat when the doors are closed and also the doors will be a bit wobbly on them due to their weight and the length of the hinges. Not partcularly impressed with slide patio doors for this application as this means one permanant fixed pane of glass . Tri fold doors was one option which fold to one side allowing for unobstruted view but they are very pricy. Maybe we should dispense with the bloomin doors altogether and allow the winter winds in as well as the summer breezes ! Now that's what I call really be bringing the outside in

(Folding doors can open either in, or out.)

Screwfix sell washered brass parliament hinges and they are affordable. Pit three on each door.

Parliament hinges can be easily cut off or the pin tapped out and the door opened. The fix is to add steel pins near the mounting screws. Drill and tap one side of the hinge fit a bolt or machine screw with head removed. Drill matching hole in the other leaf of the hinge. Now when the door is closed the pins mate into the holes and the door can't be removed by cutting off the hinge.

Parliament hinge or no parliament hinge ? That, is the question ...

I'd love one of those bi-fold/ tri-fold doors. Does anyone know where I can get one for under £1000 ? Significantly under preferably Someone is offering to make me two standard wooden double glazed doors plus a window inclusive of labour for just over £1000. By comparison these ready made tri fold doors, some starting a t £ 1700 just for a couple of doors, extortionate !

Rogerwhit, Do you mean both doors sliding back along a track with no fixed pane ? This was something I had originally thought of, are such doors easy to acquire ? The lack of security with parliament hinges is a bit of a worry, though CWatters suggestion could well remedy this. Not sure about your suggestion , Richy, the ancient tee hinges. Sounds a little complex, also it might be a bit of a hassle each time the doors are opened.
Thank you, Keith, for the info on the Screwfix hinges. However, from thier catalogue I note their parliament hinges are 152 mm - w Max. Measuring the measurments of my conservatory frame to the edge of the external window cill is just over 21 cm. I am still toying with the idea of having extra large frames installed so that they jut out a couple of inches beyond the rest of the conservatory. This way more secure smaller hinges can be used to open the doors right back. My idea has not been met with much enthusiasm though from the various builders/ carpenters I have discussed this with. They say the doors will stick out beyond the protection of the roof, but surely this can be remedied with an additional wooden structure above the doors ?

Storm, yes - a pair of slide-asides, using normal patio door gear - a lot cheaper than folding-sliding gear. But is there clearance there for them to operate?

TheDoctor's pivot would be just as economical.

I'm thinking made-to-measure in both cases for the joinery - the operating gear is available off the shelf though.