I have always taken the view that, if something is not my fault, I should, as soon as possible, be returned to the position I was in before the incident. So, if I were sure of my facts, I would hire a Motorhome (for reasonable periods of time) and claim from the other party's insurer, if necessary using the Small Claims procedures. By all means inform both insurers but do not seek permission.
Formal complaints leading to Ombudsman submissions take too long and should be viewed as a means of gaining recompense if all else fails.