well, the key things are your itinerary and your return ticket. If you manage to tell them how long are you going to be there for, what's the purpose of such trip, information of accomodation/hotel (booking confirmation), places to visit (clear itinerary, including if you've booked any trips with the local agency if not your own plannings) and the return ticket & date, you will go through the immigration without any problem ! They never dwell into how much ££ you have ! Unless you've not a clue what you're going to do in the UK !

Still don't get it why there are so many being sent back, when you're here to visit.