You should tag, chip or whatever they call it, your guitar. You should also not tell anyone that it is worth a lot of money.

Realistically, if the instrument is going to be at risk (if, for example, you were going to leave it in a tent), you would not get insurance. If the instrument is not going to be at risk (if, for example, you were travelling with a band or orchestra and there was always someone looking after the luggage and instruments), you would not need insurance.

You should consider taking a £100 guitar on the trip if it going to be at risk.