3 Amigos - brake light switch?

Hi - 3 amigos appeared initially intermittently on my wife's Y reg Freelander TD4, however they are now on permenantly. Having read the various articles here it seems that there are a few expected causes, one of which is the brake light switch.

When the problem first appeared (intermittently), it was always when the brakes were pressed that the lights came on (not every time the car braked, but every time the 3 amigos appeared it was while braking). This suggests to me that it is quite likely in this case that it is the brake light switch, however the brake lights themselves are working perfectly.

If the switch was at fault would the brake lights not be faulty too, or is it possible for a fault in the switch to cause the 3 amigos without impairing the brakelight functionality?

A diagnostic was run at a garage which indicated faulty sensors, but am I also correct in assuming that these diagnostics can be quite misleading?

Bottom line - is it worth my while replacing switch? I'm no mechanic, but I don't mind getting my hands dirty with simple things!

Yes the brake lights can still work when the switch causes warning lights to come on. The brake light switch is only a possible cause on the early abs system though, identified by the fact you have to drive to get the abs light to go off.
That said, given the age of the vehicle and the fact that now you have permanent warning lights you could have additional faults re the wheel sensors.
If yours is post 2002my I would change the switch as it's cheap and easy and see if it clears the fault, if not then go on to investigate the wheel speed senors shown by the diagnostic.