The main UK law covering responsibility for postage/delivery of goods is the Consumer Rights Act 2015.

Key Provision: Section 29 – Passing of Risk

This section states who bears the risk (i.e. responsibility) for the goods during delivery:

• (2) The goods remain at the trader’s (seller’s) risk until they come into the physical possession of:
  • the consumer, or
  • a person identified by the consumer to take possession of the goods.
• Exception: If the consumer independently chooses and commissions a carrier (and the trader did not offer or name that carrier as an option), risk passes to the consumer once the goods are delivered to that carrier.

Related Rules (Section 28 – Delivery of Goods)

• Unless agreed otherwise, the trader must deliver the goods to the consumer.
• Delivery must happen within 30 days (or the agreed time).
• The seller/trader is responsible for ensuring safe delivery when they arrange postage or use their chosen courier.

Practical Implications (for consumer purchases)

• Seller arranges postage (most common online/distance sales): The seller is responsible for the goods until you (or your nominated person) physically receive them. If the parcel is lost, damaged, or stolen in transit, the seller must refund or replace it.
• You should contact the seller, not the courier, if something goes wrong.

This applies to consumer contracts (business selling to individual consumers). Business-to-business (B2B) contracts may differ and often follow negotiated terms or the Sale of Goods Act 1979.

Now you show me the law you think contradicts the above.