ABS

Hello Grant,

The clue of your problem probably lies in your recent activity.

Check for any damaged cabling or connections at the wheels, if you have done some wet off roading or have been Fording, you could have clogged up ABS ring gears or dirty sensors - wash off the mud at clean the ring gear. 
some model have a ABS switch which can be used to knock out ABS function, if fitted, check to see if it switched on, hence disarming the ABS system.

Failing these checks, you then need to have each sensor checked out to see if any have become faulty.

Cheers,

 I go with the ABS switch theory, I have done it in the past! Even try switching it on and off with the switch.