Found the problem. I had cut and paste the line "sudo apt-get install uuid-dev" and it had a space in it. Took the space out and it worked.
Unfortunately I then hit another problem with make:-
mosquitto.c: In function âmainâ:
mosquitto.c:275:101: error: expected expression before â,â token
mosquitto.c:290:54: error: expected expression before â)â token
mosquitto.c:368:88: error: expected expression before â)â token
Makefile:15: recipe for target 'mosquitto.o' failed
make: *** [mosquitto.o] Error 1
make: Leaving directory '/home/pi/libwebsockets/build/mosquitto-1.4.2/src'
Makefile:21: recipe for target 'mosquitto' failed
make: *** [mosquitto] Error 2
One of those days today!