Here is a link to a very handy guide produced by the RHS on selection and use of Pesticides in the home garden.
You can click here to get to to the relevant PDF on the RHS website
You can buy a range of pesticides here at Agratech
Just despatched an order to RHS Wisley so thought it was an opportune time to mention they have a Grow-Your-Own weekend taking place 23-24 March.
and you can buy some plants to get you started at the Spring Plant Fair.
More Info from the RHS website here
Pic courtesy RHS website