Is it really big problem just to fax insurance certificate from HDQ to the nearest fax machine around particular aircraft?
Have no idea what are UK CAA regulations on this matter, but under JAR OPS 1.125 the fax copy of certificate is fine...
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JAR–OPS 1.125 Documents to be carried
....
(6) [The original or a copy of the] Third
party liability Insurance Certificate(s).
.......
Appendix 1 to JAR-OPS 1.125
Documents to be carried
See JAR-OPS 1.125
In case of loss or theft of documents specified in
JAR-OPS 1.125, the operation is allowed to continue
until the flight reaches the base or a place where a
replacement document can be provided.