Thank you for this question, as it made me go and learn more about this little known material. Woodwool is in its most basic form simply shavings of timber. These can be cut to a range of thicknesses, from very fine to very coarse, and a range of wood, from freshly cut to dried and stored timbers can be used.
The most common use of Woodwool is in packaging, although as with your prospective house, it can be used in a range of building products too, ranging from the slabs you mention, to slabs to be used in decking, insulating boards and even roof slabs. Having said that, it seems to be more commonly used in buildings in hotter and drier countries like Australia, Tasmania and India.
It is certainly an environmentally friendly material, as it will mulch when disposed of, and it’s good for the earth. Whether it is good for the environment that timber is rapidly grown, cut and new saplings planted (the process of rapid forestation for commercial logging) are another matter. It will be interesting to check with the Tree Council UK and Sustainable Forest groups on how they view planting and logging for Woodwool production.
One of the main issues with Woodwool is that the younger the tree that is used for creating Woodwool, the higher chance that the woodwool will retain moisture, if the tree has not had the chance to air out thoroughly. When it is used as a building material this of course over a period of time could become a problem, and I think in the this case, with this house dating from 1956, it is important to have a thorough survey of the property undertaken, with special attention being paid to this material. Given that the house is over 50 years old, they may well be in very good condition. But if there were any sign of damp on the panels then most decent surveyors or builders would recommend they be ripped out and replaced.
Woodwool is certainly a safer material to have in the home than asbestos, which is now banned for its use as an insulation material. Woodwool also could be flammable, but my guess is that these panels were treated at the time, and have lasted well. The best plan of action though is to mention the panels to your surveyor or builder or buildings inspector, and make sure they are thoroughly checked out for signs of damage, damp, or ageing.