Be careful with specific trackday cover from third party insurers Si.

Many do not know that it generally excludes liability to other participants, to any third parties or to passengers or any property damage.

So if you hit someone else (or they hit you) your not generally covered.
Same if you take out 200 metres of barrier etc, it will end up coming from your own pocket in most cases.

www.moris.co.uk maybe worth another shot, or certainly a quote.