Gfk says sales of slug killers are up 78 per cent this year so far compared to the same period in 2013.
The RHS has tweeted a warning to amateur gardeners. Advisory service head Guy Barter said: "With the high population now, if there's another wet summer slug and snail numbers will reach plague proportions, like in 2012.
"What do you expect when there's been a mild, wet spring and winter. In 2012 slugs and snails were dreadful but in 2013 it was cold then hot and dry so numbers fell.
"This year, the eggs laid in June will be doing damage in your garden by August. They breed very fast when it's mild and wet. Damage is particularly bad because gardeners are planting young plants out. Older plants can manage a bit of chewing but younger ones are quickly destroyed.
"We've tweeted a warning but it's good news for manufacturers of slug killing nematodes - they're increasing capacity. Becker Underwood who have a big manufacturing place in Sussex say they won't run out like they did in 2013."
Barter recommended nematodes, which eat the molluscs when watered onto infested gardens, and ferric phosphate slug pellets.
Barter added: "Our entomology department is dealing with earlier and greater numbers of aphid enquiries than expected. Reports are the same as in July 2013. They're always one of our top pests but this year they're higher than ever."
This spring has been the third warmest on record, while the forecast for June is for more warm and wet weather.