The much maligned Simple Delivery can't be used for items of that value so they have to go on the old system.
You certainly need to do your research on just what compensation a particular company offers and the circumstances under which they'll pay it. Most couriers have longs lists of things they won't pay compensation on so find and study those.
Royal Mail Special Delivery can be bought with cover up to £2,500 with relatively few exclusions for items up to 20kg and 61cm x 46cm x 46cm (44 lb and 24” x 18” x 18”).
Cacas vendit.