Should I use spray foam to insulate my 1960 house with solid walls?

My 1960 built house has solid block walls dry lined on inside nailed to studs with a 5" air gap. The ground floor is suspended with a solum 3 ft deep and a dirt floor, ventilated by air bricks. The suspended floor is insulated with fibreglass roll stapled below. 

The cold attic is ventilated with fibreglass roll on the ceilings. No air barrier of VCL. Cold air is free to flow from solum to attic via the air gaps in the walls Temperate climate, about zone 5, avg annual rainfall 30" avg temp 8 C. The house is cold, a lot of heat is lost through the walls.

I contacted spray foam contractors who propose to spray foam to onto the suspended floor and under the roof ( converting to warm attic), pouring foam in the air gaps in the walls from holes drilled in the dry lining. The foam will form an air seal envelope and insulate. They say the foam is permeable. I think spraying the suspended floor is ok because the insulation is on the outside, making the floor is warmer, so no part of the structure is below the dew point temp.

But I'm concerned about condensation in the walls and roof, the outer fabric will be colder and there is no air gap behind the foam for ventilation. The foam may be permeable, but I'm unconvinced that any water could get out. There is experience applying these techniques in stately homes with solid walls and lath and plaster linings in this location, but info is scant. I can't afford to wreck my house due to condensation and rot.  What do you think? thanks, Alan Chesterman