found this here
http://www.churchill.com/general/site_help/car_faq.htm
Do you provide cover for trailer tents?
Our policy covers, on a Third Party Only (TPO) basis, any vehicle insured by us for towing a trailer (including a caravan, trailer tent or horse box) or disabled mechanically propelled vehicle (i.e. towing a broken down car) as allowed by law. However, we are not liable for any claim arising from loss of the towed trailer or vehicle or property being carried in or on the towed trailer or vehicle and while such trailer or vehicle is being towed for reward.
The way I read this, is that the Churchill will not be liable for the broken vehicle that is being towed in the event of any damage it may cause.
Check your insurance to see the small print