Sarah's pondlife - do what happymarion says! If you want a wildflower meadow you will need to remove the top layer of soil as it is too rich for wildflowers (unless there are already wildflowers growing there?). Grass can smother wildflowers so I wouldn't advise you to sow wildflower seed, especially in turf.
If I were you I would first sow some wildflower seeds in plugs, so they become plug plants. (Do you get Gardeners' World Magazine? There is a project on making wildflower plugs in the April issue.) Or buy them from reputable suppliers, like Wiggly Wigglers as happymarion suggests, or Habitat Aid.
While the plugs are growing on, remove the top layer of soil, exposing the subsoil beneath (which is usually lighter in colour), then plant the plugs and sow grass seed at the same time, to give the plugs a head start. Include yellow rattle in the wildflower mix as it suppresses grass growth, helping the wildflowers thrive. Annual wildflowers should flower this year if you're quick, while perennial ones will flower next year if you sow them now. Hope this helps!
Kate