5 pounds a week is going to get a pretty hard knock from maintaining a nano tank. Have you checked at maidenhead aquatics or another local shop what they think a 10 gallon nano setup will cost? You will need to find a good retailer and stick to them for help when things go wrong.
Do you get practical fishkeeping - philip hunt just did a good 4 part series on keeping a marine tank 'sensibly'. Guess what a 90 cm tank cost him about 700, though you could beat it down. Even a good book will hit you for 30 on amazon.
Being harsh cheap and uncomplicated do not mix well in saltwater. Prices in (), shop around and you should get these prices
You need a tank(15), hood (20), heater (15) , oolitic sand (5) or coral sand, don't worry about it not being live. You will need 10 lbs of live rock (50). You will need saltwater , so water + salt (20 to start). Water we will come to. You will need a hydrometer to test salinity (5) and at least test kits for ammonia, nitrite, nitrate.(30) Get a gluval 3 and stuuf it with carbon (20 + 5), and get another to help circulation(20). Lights are a nightmare, just use a white daylight tube or 2 in the tank hood, and FORGET anemonaes and most corals (20).
You say you don't want a skimmer. So instead you can do a weekly water change (money for salt, say 1 a week). You also need water, and basingstoke tap water is NOT good enough for this - you need RO. If you have a good local shop they might be selling RO, else they might even sell premixed water, because you might find mixing water a hassle.(bucket 2). You HAVE to do water changes at least once a week if you don't have a skimmer, and probably once a week anyway a week if you do have a skimmer.
Are you parents prepared to drive you around once or twice every week with buckets of water, as it will be hassle to buy 4 or 5 at a time (you'll need to heat it an circulate it anyway to keep it good).
Really go to your lfs and cost this properly otherwise you're eading for a pricey disaster.
Sorry this is so discouraging. Eee, when I was you age I was breeding firemouths. But because a 10s so small it needs a lot of looking after, and that love isn't always cheap