You could do one of the Minwax wipe-on poly gel and stain products.
For an all-in-one color and hard finish product:
http://www.minwax.com/wood-products/preparation/minwax-polyshades
You can topcoat the Polyshade product with Minwax's Wipe-On Poly product if you want more layers of clearcoat once you've locked in the color you want.
Alternatively, this water-based product looks simple and easy to use, and has a product-specific clearcoat you can put on top of the color (NB: I haven't used this, but if I were starting out, I'd experiment with it):
http://www.minwax.com/wood-products/one-step-stain-and-finishes/minwax-express-color-wiping-stain-finish
I don't know whether these products are available in Merrie Olde England, but this will give you an idea of what kinds of finishes are available to accomplish what you're after.
Note that alder does not play well with thin oil or water based stains unless you condition first with a very thin wash coat of shellac or a comparable product - otherwise you may wind up with disappointing blotchiness in your color coat.
For that reason, perhaps a tinted toner might be a better approach than a stain-with-clearcoat approach.
As always, you will be best served by doing a trial run on scrap lumber of the same species as your guitar body.
Bagman