Since 2025, it seems UK shares are off to a good start, with the flagship FTSE 100 index up by almost 5%. Yet, not every British enterprise has had a great time of late.

In fact over the last six months, there have been some pretty heavy losses incurred by some well-known brands.

Britain’s worst five performers

Looking across the FTSE 350, the worst-performing UK shares over the last six months are:

1. John Wood Group, -67.8%
2. Vistry Group, -54.6%
3. Aston Martin Lagonda, -43.6%
4. JD Sports Fashion, -43.3%
5. Greggs (LSE:GRG), -41.4%

At a quick glance, there doesn’t seem to be an overarching theme across these businesses. Each operates in fairly distinctive industries, including engineering, homebuilding, automotive, fashion, and baked goods. And yet a £100,000 equal-weighted portfolio diversified across these five companies would now be worth around £49,860 – a near 50% crash.

What went wrong?

There are a lot of factors behind these lacklustre results. While some may be external in nature, there could also be some internal issues and mistakes being made by management teams. Let’s zoom into Britain’s favourite bakery chain, Greggs.

While the stock’s been fairly volatile over the years, the underlying business has a fairly impressive track record of sating customer appetites. Extended trading hours, the expansion of its store footprint, and new product launches have all contributed to Greggs’ 20% annualised revenue growth rate, with profits following behind. And even in 2024, it delivered record results surpassing £2bn in sales for the first time in company history.

So why is the stock down over 40% since September? It seems the first few weeks of 2025 are off to a rocky start, with like-for-like growth seemingly evaporating. Management’s putting the blame on bad weather, but the group’s steady stream of price hikes could also be contributing to declining sales as consumers look for cheaper alternatives.

Pairing this with the incoming rising costs from higher national insurance contributions, investors are getting understandably spooked.

Turnaround opportunities?

Often, some of the best UK shares to buy can be those which have fallen out of favour. Such businesses can end up getting oversold, creating terrific buying opportunities, even with headwinds plaguing operations. Is this the case with Greggs?

Slower growth among uncertain economic conditions isn’t all that surprising. However, it could be a big problem if the cause of slower growth is shrinking interest from customers due to higher prices. Further price hikes are likely on the way as staff costs rise, which may push sales growth into the red.

Right now, it’s too soon to tell whether weak trading in 2025 is due to a temporary blip like bad weather or a more fundamental issue. So until some much-needed clarity’s provided, this isn’t a business I’m rushing to buy. Of course, should sales performance start to recover even as the price of a sausage roll rises, then I may have to reconsider.

As for the other UK shares on this list, investors need to investigate each carefully to decide whether they’re a screaming bargain or a giant red flag waving people to stay away.