1.9m would be very tight to convert, but it does make a difference where the measurements were taken from.  You would need a minimum of 2m from the top of the ceiling joist to the top of the ridge board ( the ridge board is the timber at the very top of the apex of the roof).  The chances obtaining planning permission for raising the ridge would be very minimal as you are a semi detached property, however there might be a possibility that part of your ceiling could be lowered to achieve a usable height at the loft level.  It would be best for our surveyor to make an appointment so he can talk to you accurately regarding if the conversion would work and the floor to ceiling / slope heights that could be achieved.