My cousin and I flew from Sydney, Australia all the way to London, England... and oh, what a flight. Twenty hours on a plane with two stops and always next to smelly people who fall asleep on me.
The whole reason for going to London though, was to meet up with our Contiki crew (which we booked from Sydney). Basically, it's a tour group led by a guide who knows the in's and out's of each city and the duration will vary depending on the tour chosen. I booked European Adventure which is available here. Unfortunately, we had the dates mixed up and missed the boat from London to Amsterdam, but alas, we were unaware. Thus we had spent the day shopping on Oxford street (which is a must whether you are a female or male). Out of all the cities I had visited, I found that London was in my top 5 places to shop! Soho was a great place to visit as well, but a little quirky... it really depends on what you're looking for. If you are the conventional shopper try going to Oxford street and Harrods but if you are out there and a little wild, definitely go to Soho. If you have the baggage allowance and you are a dressmaker, try going to the Cloth House (98 Berwick Street Soho).
I suggest if you only have a limited time in London, hop on the Big Bus Tours as it will take you to every famous location in London. This was originally planned for day 2 in London in which we never experienced.
The theatre is also great to see, personally I would suggest 'The Lion King' which was spectacular (in my opinion you can never be too old for a Disney production). It was a small theatre with an immaculate design and a safe location to walk around during the night. Meanwhile the next morning, on the way to the Big Bus Tour pick up point, we had dropped into the Contiki office to make sure our timing was right. Sadly, we had to rush to the airport after booking tickets for a flight that day only to find out when we arrived that we bought tickets for the 7th of july instead of the 24th of June. The lesson here I guess is to take your time so little details such as the date are not missed. 300 pounds each later, we boarded on the correct flight and made our way to Amsterdam...