One of the most celebrated combinations — and one of the more evidence-supported ones. Basil planted near tomatoes appears to deter aphids and whitefly, and the aromatic oils may improve the flavour of nearby tomatoes. Both plants also have similar care requirements (warmth, sun, water) so they're practical to grow together. Plant basil around the base of tomato plants or in the same bed.

The classic Native American combination. Sweetcorn provides a climbing frame for beans, beans fix nitrogen that feeds the corn and squash, and squash leaves shade the ground to suppress weeds and retain moisture. It's a genuinely elegant system that works well in larger plots. Requires good spacing and a warm summer to work well in the UK — best in a sheltered, sunny spot.

Carrot fly and onion fly are both deterred by the scent of the other crop. Growing carrots and onions in alternating rows is a traditional combination with genuine logic behind it — the mixed scents confuse the pests. Not a complete solution (barrier fleece is more reliable) but a useful additional measure.

Nasturtiums act as a trap crop for aphids — the aphids preferentially colonise the nasturtiums rather than your cabbages and kale. You can then destroy the aphid-covered nasturtium plants or simply let predators find them. Plant nasturtiums around the edges of brassica beds.

Chives, garlic and other alliums planted around roses are widely believed to deter aphids and black spot. The evidence is largely anecdotal but the combination is attractive and low-risk — alliums look good under roses and the occasional harvest is a bonus.

French marigolds (Tagetes) are the most versatile companion plant in UK vegetable gardens. Their root secretions suppress nematodes in the soil, their scent deters whitefly and their flowers attract hoverflies and other beneficial insects. Plant them throughout the vegetable garden — they're effective, cheap, long-flowering and cheerful.