* Block the outside of low airbricks - batten frame stuck on with adhesive such as Wet Grab (from Evo Stik) which is flexible and can be applied even to wet surfaces. Then a screw-on plywood panel sealed and applied to the top of the frame.
* Block downstairs toilets - not sure how, though. A stuck on board would do if nothing better.
* Block the bottom half metre or so of each external doorway - basically plywood panels sealed onto and screwed onto a U-shaped frame made of battens. The batten frame could be stuck to the doorframe with adhesive.
* Above the door plywood panel have 20cm or mor of water filtering sandwiched between chicken wire or similar.
The idea of restricting the height of the door panel (and having a filter on top) is to limit the pressure that outside water can apply sideways to the wall. Better to flood than to have the wall pushed in. I'm not sure what height a wall could be expected to support. The above "half metre or so" is a guess at what should be safe. Any higher water could flood in but be to some degree filtered.
The above is meant for water coming down the street. Cannot think of a way to deal with water coming up through the ground.