I meant to post this a couple of days ago, but never got around to it....

Whilst driving at fairly low speeds in town my wife applied the brakes and found the pedal went to the floor. She was going slow enough to pull the handbrake on to stop the car, and she then contacted the garage who picked the car up. It turns out that the rubber seal on the rear brake had split allowing all the fluid out..... The worrying thing is that at no point has the on board computer mentioned the brake fluid is low, even when it was totally drained, and yet it feels the need to tell us random levels of oil and error messages about diesel humidity thingys!

Anyway, £360 later and the car is back on the road!

**** happens.
But it's almost impossible the splitting rubber you described caused this.
Every car has a double brake system, so when one system failles, the other works (although you have to pres harder to stop).
I think it's more likely your master cylinder has gone bad....this has the effect you mentioned.

I had a rear wheel cylinder start chucking out brake fluid,but it was a leak not a flood,and I did get a bleep and brake fluid low warning on the dash,cant see why you didnt. I changed both cylinders and shoes myself,I'm sure parts from a dealer were less than £100 and a couple of hours for me to fit.....£360 sounds a lot.

When my brake fluid disappeared due to the handbrake cable abrading through a brake pipe, there were no warning lights, bleeps or anything else. Just no brakes!

As for dual braking systems saving your bacon, hmmm.

Has anyone had a brake fluid low warning bleep.....I'm certain I did but after Zundapps post beginning to think I imagined it......

There should be some kind of floating electrical mechanism under the filler cap.
Unscrew it, take it up and see if the light comes on.....
(be careful with the brake fluid, it's very aggressive to paint!!)