Thanks for the helpful comments, as well as the wise-cracks.
The window is a rather large upvc bay window, from a good manufacturer and well fitted. Not sure we want to the cost and hassle of taking it out all for a sofa!
Please can someone advise with a viable solution.
It's a long story, but after some building alterations a while back, our sofa is 'land-locked' in the lounge. It's just a bit too long to get through the internal door, no matter what angle you take. (This was known at the time of the building...