Royal Mail 1st Class (1-3 days) and 2nd Class (3-5 days) are insured* to £20. The Signed For versions of each are insured* to £50, have tracking and a signature on delivery.
Royal Mail Tracked 24 & 48 (1 day & 2 days) are insured to £150, have full tracking and notifications.
Guaranteed (Next Day) Delivery has insurance - including damage cover to antiques, ceramics and glass - to £500, tracking and a signature on delivery.
*loss only with antiques, ceramics and glass - no damage cover to such items with these services.
I no longer have a viable post office, but thankfully Royal Mail are currently collecting from domestic addresses for free.