Part of any safe railway design is to ensure vehicle incursion isn't possible where roads are located nearby. This includes protecting the perimeter by use of obstacles and secure boundary fencing. The issue was due to poor integration and on that part both NR and Highways are culpable.
The design flaw had been there for some time, however as with all safe systems you dont stand still and say its been ok so far. It wasn't the first incident of vehicle incursion onto the railway, but it was the first to be struck by a high speed train. From a risk mitigation point of view the cost of preventing the incident by use of a suitable vehicle restraint system or obstacle was disproportionately small relative to the value per fatality. However at the time Railtrack and its infrastructure maintainers were focused on profit rather then ensuring the system was safe and updated.
Being able to identify and resolve these issues requires very detailed knowledge of the railway something that people who work day in day out on certain route sections know.
Getting rid of that knowledge via swathes of job cuts undoubtedly will make the railway less safe. Paying for that knowledge on safety critical infrastructure via the private sector isnt a cheaper option. Want a senior safety engineer? The going rate is about £150 per hour to a client. Signalling principles checker around £200 per hour.