This phenomenon affects some people more than others but is on the rise. You get a text in offering “No win No fee” court case for an accident (which you haven’t actually had). Alternatively you get “Did you take out a bank loan prior to 2009? You are entitled to £2300 in compensation”. I could go on.
In this case the first thing you should do is contact your mobile carrier and get them to block these crooks.
DO NOT REPLY TO THE TEXT. Do not send stop or any other response as this just confirms to them that the number is valid and that their first text got through.
You can also contact the UK Information Commissioner here.
PS a colleague has mentioned receiving texts from a remote user who appears to be using an old phone that may have been sent to recycling. This shows the importance of completely wiping phones before you pass them on.