Please could someone tell me why I should be really worried about Brexit with no deal

I absolutely agree Gill

Countries who made no preparation (for Y2K), one of which was Russia, had no problems.

Sorry, minniemoo. A quick google revealed that Russia did make preparations, often with help from the US. Not as intensively as some countries, but certainly didn't ignore it.

One article noted that one of their 'fixes' was to turn computer 'clocks' back to 1970... could be interesting in 10 years time if the amended programs still exist...

I was just wondering why Russia was used to back Minniemoo's unsupported suggestion. Has she a source we don't, perhaps?