. The two beams holding up the attic floor are not connected to the A frames which is a bit of a lost opportunity for imparting some strength to the roof.
In the second place the horizontal beams in the A frames are mortice and tenon joints secured with wooden dowels. In compression this is very strong as the shoulders of the joint butt up against each other but in tension the strain is taken on the weak wooden pegs which break and allow the A frame to do the splits pushing the tops of the walls out.
Alternatively, the problem is down to lack of maintainance of a stucture built back in 1835:
A Corrugated iron roof has replaced the old cotswold stone tiles which were probably sold long ago. It is also possible that the original roof was thatched. At least corrugated iron is very light putting less strain on the roof timbers and walls. Unless of course the weight of a stone roof pinned the A frames into compression hence keeping the whole structure in shape