Sorry to be apain, but there is no engine size (my fault). I've assumed it's a 1.4, but the values won't differ hugely regardless of engine size - you'd be talking about �200 either.
Average mileage for the year would be 79000. At 120k, the values would work out to �1725 retail, �650 trade. Obviously this is not taking into account pre-accident condition, so it could be adjusted either way again. These figures are also from May - someone has taken my more recent guides, but figures suggest prices are remaining quite constant, so you may see a �50 drop over the two months.
As a general rule we will move cars immediately to our salvage yards mainly to avoid any possible storage charges - if the car is drivable, there is nothing stopping you keeping it until a settlement figure is agreed. The cars are usually sold on at auction by the scrapyard (dependent on the category) to be repaired or for spares. Typically, a lot of cars with damage like your son's just go straight back on the road.
Have they actually inspected/estimated the damage? We make a lot of decisions to move the car straight to salvage on age/value/damage reported - I would have said your son's car is a border-line economic total loss as it will likely need a respray up the entire side, plus unknown parts.