What’s more, the concentrations of neonicotinoids were similar to those found in treated agricultural crops, concentrations that have been shown in other research to have harmful effects on bees. Other contact poisons, such as chlorpyrifos and pyrethroids, were found in fewer plants, but sometimes at high concentrations.

It’s impossible to say how much harm these plants might do to the pollinators in your garden. A few of them, among large numbers of uncontaminated plants, would probably do no harm at all. But if you planted up a whole bed with contaminated plants in spring, they might deliver a big dose of pesticides at a critical time in the growth of new bumblebee nests.

The good news is that Aldi, one of the retailers involved, says it stopped using neonicotinoids in October 2016 (the plants tested were bought in July 2016). And B&Q has announced it will not allow its suppliers to use neonicotinoids from February 2018. But that still leaves a few other unpleasant chemicals, so the safest option is to buy your plants from an organic nursery (see the RHS list here), grow your own plants, or swap with like-minded friends.

The RHS ‘Plants for Pollinators’ logo is one of the best guides to the right plants to grow for pollinators. However, the RHS has no control over how plants are grown by retailers and, in the light of this research, they are reviewing the scheme in case they need to make changes.