Example: "Free Msg: Our records indicate you may be entitled to £3750 for the accident you had. To apply free reply CLAIM to this message. To opt out text STOP".
Do not reply to this - you could well receive a flurry of texts for which you will be charged significantly.
Do not phone the number - you could well be charged premium rates for the call to listen to a recorded message.
What to do? Register a complaint with the Information Commissioner at https://www.ico.gov.uk/Global/contact_us.aspx, saying, for example, "I wish to register a complaint about this message as I believe it to be unlawful as well as a scam and a nuisance." Give the time, date and phone number of the sender as well as the message text itself. If enough people complain, the ICO may have enough ammunition do do something about it.