John Lewis said its boss was stepping down and Marks & Spencer shares have slumped after both retailers delivered grim Christmas trading updates.
Each saw sales fall over a tough festive period for the high street - capping a gloomy 2019 which was the worst on record for the retail sector.
Supermarket giant Tesco bucked the trend, but even then only managed to eke out growth of 0.1%.
At John Lewis, the departure of managing director Paula Nickolds was announced as it reported like-for-like sales down 2% for the seven weeks from 17 November to 4 January and warned of lower profits.
Meanwhile, beleaguered Marks & Spencer - relegated last year from the FTSE 100 - saw shares fall as much as 10% after it reported another decline in clothing sales and weak online growth.
It said it was affected by "disappointing one-off issues" including buying too many pairs of skinny jeans and waste in its food business.
John Lewis Partnership (JLP) said the departure of Ms Nickolds was the result of a shake-up integrating the teams behind its department store brand John Lewis - which she currently leads - and its supermarket chain Waitrose.
Ms Nickolds, who has worked at JLP for 25 years and has been managing director of John Lewis since 2017, will leave the partnership in February.
Christmas trading figures showed a stellar performance for John Lewis over Black Friday, when sales rose 10%.
But that could not be matched over the rest of the festive period when the chain saw "more subdued demand" - and annual profits are now expected to be "substantially down on last year".
Sister brand Waitrose did better, with sales up 0.4% despite a weak grocery market, but the overall partnership is still on course to report underlying profits "significantly lower than last year".
Chairman Sir Charlie Mayfield warned that the board will have to decide next month "whether it is prudent" for the employee-owned business to pay its usual annual bonus to its 80,000 partners.
That was similar to a warning given last year - and though in the end there was still a staff payout, it was the lowest by the company for 66 years.
There were more bleak figures from M&S, which has been struggling for years to reverse demand in its clothing and home ranges.
Chief executive Steve Rowe said there had been a "strong start" to the quarter - covering the 13 weeks to 28 December - followed by a "challenging trading environment in the lead-up to Christmas", leaving like-for-like sales down by 1.7%.
M&S said womenswear showed "signs of continuing recovery" though menswear and gift offerings struggled.
But the retailer's online revenue growth, at just 1.5%, was weaker than expected - blamed partly on discounting by rivals in December.
Marks's food division was a bright spot with like-for-like sales up 1.4% - after what it described as a "standout performance in the two-week Christmas period".
For Tesco, Britain's biggest supermarket, UK like-for-like sales climbed 0.1% in the six weeks to 4 January though over a longer 19-week period stretching back to August, sales were down 0.2%.
Chief executive Dave Lewis, who is due to step down later this year, said: "In a subdued UK market we performed well, delivering our fifth consecutive Christmas of growth."
The performance was better than that experienced by rivals Sainsbury's and Morrisons, which both saw sales decline over the festive period.
Tesco shares rose 3%.
The update comes after supermarket industry figures suggested households tightened their belts, resulting in the slowest Christmas season growth for the sector since 2015.