Actually, what you're wishing to do is the same thing we Bonsai growers accomplish to keep our plants minaturized.
However, simply pruning the branches won't help you more than a few seasons at most. To truly restrict the growth as you describe, not only will you need to prune the branches during dormant season, but you'll need to remove the root ball from the pot. After pulling it up, gently comb it out with a hand garden rake... you know... the small ones you use to weed around the base of plants. Once the roots are loosened, cut about 1/4 to 1/2 of them back. (There are actually Bonsai scissors for the purpose, but any good shears will work.) Don't just trim the whole ball by that amount, but actually remove that amount of roots, cutting back near the base of the plant.
Replace the plant in a good potting soil and water generously for a few days. The root treatment can be done during the growing season, but can also be done during the dormant stage.
You'll only need to do this once every two years or so. Another hint... after you comb and trim the roots, give them a good squirt with the water hose (as we call it here in the U.S., think you Brits call it a hose pipe, no?) rinsing some of the dirt out.
After the intial watering after transplant, don't over water and don't over fertilize... just a little of both...
Good luck!