Put it into a mutual fund that follows the S&P 500. The S&P 500 is the top 500 US companies. The returns on the S&P 500 are usually very good, and make an excellent, low-risk long-term (5 years or more) investment.
If I were you I would probably put £25k in the S&P 500 (I would suggest a more diverse portfolio, but you've said you don't really want to spend time managing something like that), and keep the other £25k in more liquid investments (meaning you can easily turn your investments back into cash-in-hand) than the S&P 500. The reason I wouldn't consider the S&P 500 very liquid is because it is a long-term investment; you have to be willing to wait through a dip in the value till it breaks through and starts making a profit again, which may take 2 years or so. You don't want to be forced to sell your stocks at a low rate when you're strapped for cash. So I would advise putting the other £25k in a mix of current accounts and gilts. Gilts are bonds to the government. A bond is where you loan someone or a company money. Bonds to the government are called 'gilts' because the government has never, ever faulted on any of its bonds. These bonds will return a dividend (payment) at the end of the each year, and can be up to 5%. After the agreed period, (say, 5 years), the government repays all of your money in full. Gilts are sold at £100, meaning after 5 years you will have £25 for every £100 you put in gilts. You don't have to wait that whole time though, and it is more usual to sell your gilts before they mature.
Don't be a miser and save everything though. There's a reason I said put the other £25k in liquid investments. You need to have quick access to it, because I want you to spend it. You're only young once. Have fun.
P.S.
Don't bother with savings accounts, they are a total rip off.