In reply to Deadeye:
You have to tell the sender if the circumstances are as described in my second paragraph, including the OP's case where goods were received by mistake and are clearly for someone else.
If the goods are truly unsolicited, ie a person did not request the goods, then they are free to keep them.
In the case here it could be argued the items for the other person were not requested by the OP and would therefore fall to be unsolicited. However, the OP did request goods from the company in question and other goods were, by mistake, included in the OPs order. These other goods are therefore not unsolicited, and as I and others have said the OP should give the company a chance to recover their goods.
Properly unsolicited goods are pretty rare now. I think some time ago some unscrupulous companies would try it on by sending unsolicited goods and then try to demand payment for them. Demanding such payment is now illegal. However, if goods are received in this way then the receiver may keep them.
This link https://en.wikipedia.org/wiki/Unsolicited_goods#cite_note-1 includes the following
"Also with effect from 14 June 2014 the distance regulations are replaced by The Consumer Contracts (Information, Cancellation and Additional Charges) Regulations 2013 which include a new s 29A added to the Consumer Protection from Unfair Trading Regulations 2008 making it clear the consumer may keep unsolicited goods"
This link - https://en.wikipedia.org/wiki/Consumer_Protection_(Distance_Selling)_Regula... includes the following definition of unsolicited goods
"If goods are sent to a consumer without a contract asking for them, the "recipient may [...] use, deal with, or dispose of the goods as if they were an unconditional gift to him"[12] and "[t]he rights of the sender to the goods are extinguished".[13] This is intended to prevent companies purporting to demand payment for goods a consumer receives unexpectedly. This provision amends the Unsolicited Goods Act 1971, which defines goods only as unsolicited goods if they have been deliberately sent to the recipient with the intention of them being used. Goods sent or delivered by mistake are not unsolicited goods, and remain the property of the sender"
Dave