Vauxhall Zafira cut out and speedo clicking?

driving my car earlier, I slowed down to a standstill in traffic, all of the dials on the dash flickered then the engine conked out.

car would not restart, made no noise at all when i turned the key. was able to close the window with keys in ignition.

Ive had the car for 3 years, flies through mot,

the dials have flickered a couple of times previously when starting but its always started with another turn of the key.

Any ideas? it was a frightening experience, luckily some kind strangers stopped and pushed my car off the road.