Raz91

Good evening everybody. I own a john laing easiform property. I have already done some tweaks to the house such as new windows all over and added 400mm Knauf insulation to the loft. Now it come the big project that i want to do. I am planning on knocking down both external and internal walls of the house and raise new walls made of block and brick with the cavity. The house its a semi detached house, 78sqm2 of liveable space, 225sqm2 in total. Would i need planning permission and party wall agreement with my neighbour to do such job? And what are some realistic figures to complete such jobs? Kind regards, Raz