Any question answered...

I have to send an item back to Switzerland for a warranty claim. The company have said this in the email containing return postage instructions:

Don’t forget to declare the content of your shipment with the green
stick-on customs label obtainable in any European post office.

When declaring your shipment: Always select the "sample" option
Declaration of value: under 18€ / 15£

They also recommened using a tracked/insured shipping method. The item is worth £250.

I thought it wasn't possible to insure an item for a value higher than the declared value on a customs form?