Thanks for your replies. Yes the USB memory stick plays on my desktop computer with no issues. I do not know who the manufacturer is, the format is FAT 32. I bought 6 from Amazon and put audio books on them to play in the car. I have tried a couple of others that worked in my previous Lexus and they do not play in this one either. I have copied the present one on to a CD which plays ok on the Lexus CD player, thank goodness Lexus have not done away with CD players yet like some other manufacturers have.
The car has come with a 12 month warranty so if I cannot cajole the USB sockets into working I will see if the Lexus garage can fix it when I take it in for a service.