to think £1700 for house insurance is ridiculous

[ChocFrogKnife]

3 bed thatched property with a wood burner but, even so, £1700 is outrageous and that’s the lowest we can find

When the thatch needs redoing there are several systems that can be installed that insurers will recognize and protect the fabric of the house including the roof joists from fire damage. Stopping the actual thatch burning is a different prospect so it may be sacrificial if a fire starts deep within it.
Worth considering building in an approved system if you can speak with insurers and see if the cost of the extra protection will be mitigated against increased insurance. (Also additional piece of mind and less disruption if something does happen and the building is 100% fine)