From someone with some life experience whose moral compass may be swayed by such experience. I would personally hold on to it. Put in a shoebox under your bed and forget about t for the meanwhile. Yes it may be exciting to be able to buy something extra-ordinary but really 7k is like one handbag to some people.
It is not a life-changing amount of money. How can you go about making use of it without telling close friends / family who will spend it for you, so keep to spending £20 at a time and mostly making additions to your normal spending.. so a new pair of shoes, you might add an extra £20 to them, you and your friends want to eat at nandos afterwards then great, just don't offer to pay £100 for the meal! The best way to burn through it is on the weekend so where you might have had £20 for the night you can can spend £50 and make good use of investing in socialising with friends and meeting new people, finding your moment to buy them a drink and be cool about it and no-one will be the wiser.
You have to remember you found it at one of the busiest train stations in the country with thousands of people going through there each day and you would be none the wiser that this money existed. It will still exist once it has gone from your hands.
You might not have had that kind of money to burn before but you will be amazed how fast it goes..
To be honest it would probably be best spent on starting your career, if you wanted to get into business, the best way to impress is a nice suit and you will have your travel costs sorted.
Remember not to deposit it in your bank account at the notes have serial numbers and the police will know where the money is.
Good luck, spend it wisely and in good time and make it do something for you.